VNX - Performance Characteristics
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Transcript of VNX - Performance Characteristics
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How do I monitor system health > Performance Characteristics
Performance Characteristics
The Analyzer Performance characteristics apply to disks/RAID Groups, SPs, RAID group LUNs (non-pool
LUNs), metaLUNs, thin LUNs, thick LUNs (traditional LUNs in a pool), VNX Snapshot Mount Points, snapshot
sessions, asynchronous mirrors, and/or front-end ports as shown in the sections and tables that follow.
There are several categories of performance characteristics. The categories available to customers are Basic
(default) and Advanced. The Advanced category includes both Basic and Advanced characteristics. You can
change between the Basic and Advanced characteristic display by selecting Customize Charts and
checking or clearing the Advanced box in the General tab. The Basic and Advanced performance
characteristics are shown in separate tables for each item.
SP
The Storage Processor (SP) processes all I/Os within the storage system, host requests, management and
maintenance tasks, as well as operations related to replication or migration features.
In Unisphere Analyzer, the statistics for an SP are based on the I/O workload from its attached hosts.
Utilization and cache metrics, however, also reflect any internal processing that is occurring.
Basic Characteristics
Characteristic Description Comment
Utilization Describes the fraction of a certain observation
period that the system component is busy serving
incoming requests. An SP or disk that shows 100%
(or close to 100%) utilization is a system bottleneck
since an increase in the overall workload will not
affect the component throughput; the component
has reached its saturation point. Since a LUN is
considered busy if any of its disks is busy, LUN
utilization usually presents a pessimistic view. That
is, a high LUN utilization value does not necessarily
indicate that the LUN is approaching its maximum
capacity.
When the SP becomes the
bottleneck, the utilization will be
at or close to 100%. An increase
in workload will have no further
impact on the SP throughput, but
the I/O response time will start
increasing more aggressively.
Queue Length The average number of requests within a certain
time interval waiting to be served by the
component, including the one in service.
A queue length of zero (which is
average) indicates an idle
system. If three requests arrive
at an idle SP at the same time,
only one of them can be served
immediately; the other two must
wait in the queue, resulting in a
queue length of three.
Response Time
(ms)
The average time, in milliseconds, required for one
request to pass through a system component,
including its waiting time.
The higher the queue length for
the SP, the more requests are
waiting in its queue, thus
increasing the average response
time of a single request. For a
given workload, queue length
and response time are directly
proportional.
Total
Bandwidth
(MB/s)
The average amount of data in Mbytes that is
passed through a system component per second.
Total bandwidth includes both read and write
requests.
Larger requests usually result in
a higher total bandwidth than
smaller requests.
Total
Throughput
(IO/s)
The average number of requests that pass through
a system component per second. Total throughput
includes both read and write requests.
Since smaller requests need a
shorter time for this, they usually
result in a higher total
throughput than larger requests.
Read
Bandwidth
(MB/s)
The average number of Mbytes read that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Read Size (KB) The average read request size in Kbytes. This number indicates whether
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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
the overall read workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
Read
Throughput
(IO/s)
The average number of read requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher read
throughput than larger requests.
Write
Bandwidth
(MB/s)
The average number of Mbytes written that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Write Size (KB) The average write request size in Kbytes. This number indicates whether
the overall write workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
Write
Throughput
(IO/s)
The average number of write requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher write
throughput than larger requests.
Service Time
(ms)
Time, in milliseconds, a request spent being
serviced by a component. It does not include time
waiting in a queue. Service time is mainly a
characteristic of the system component. However,
larger I/Os take longer and therefore usually result
in lower throughput (IO/s) but better bandwidth
(Mbytes/s).
Larger requests usually have a
longer service time than smaller
requests.
Characteristic Description Comment
SP Cache Dirty
Pages (%)
Advanced Only
Percentage of cache pages owned
by this SP (pages committed to
cache, but not yet written to
disk). In an optimal environment,
the dirty-pages percentage will not exceed the high watermark
for a long period.
This metric shows the level of the write cache at
the last poll time and is not as an average over
the last polling interval.
SP Cache Flush
Ratio Advanced
Only
The fraction of the number of
flush operations performed
compared to the number of write
requests. Since the ratio is a
measure for the back-end activity
compared to front-end activity, a
lower number indicates better
performance.
A flush operation is a write of a portion of the
cache to make room for incoming write data.
SP Cache MBs
Flushed/ s
(MB/s) Advanced
Only
The number of megabytes per
second written from the write
cache to the disks.
The value is a measure of back-end activity.
SP Cache High
Water Flush On
Advanced Only
Number of times, since the last
sample, that the number of
modified pages in the write cache
reached the high watermark. The
higher the number, the greater
the write workload coming from
This number will only increase if the percentage of
Dirty Pages has previously reached the low
watermark.
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Disk/RAID Group
As the slowest devices in a storage system, disk drives are very often responsible for performance-related
issues. Therefore, we recommend that you pay close attention to disk drives when analyzing performance
problems. RAID Group values are an aggregate of their disk performance values.
Basic Characteristics
the host.
SP Cache Idle
Flush On
Advanced Only
Number of times, since the last
sample, that the write cache
started flushing dirty pages to
disk due to a given idle period.
Idle flushes indicate a low
workload.
SP Cache Low
Water Flush Off
Advanced Only
Number of times, since the last
sample, that the number of
modified pages in the write cache
reached the low watermark, at
which point the SP stops flushing
the cache. The higher the
number, the greater the write
workload coming from the host.
This number should be close to
the High Watermark Flush On
number.
This number will only increase if the percentage of
Dirty Pages has previously reached the high
watermark.
SP Write Cache
Flushes/s
Advanced Only
Number of times per second that
the write cache performed a flush
operation. A flush operation is a
write of a portion of a cache for
any reason; it includes forced
flushes, flushes resulting from
high watermark, and flushes from
an idle state. This value indicates
back-end workload.
A flush operation writes contiguous data out to
disk. This includes forced flushes, flushes resulting
from watermark processing, and flushes due to
idleness.
Average Busy
Queue Length
Advanced Only
Average number of requests
waiting at a busy system
component to be serviced,
including the request that is
currently in service.
Since this queue length is counted only when the
SP is not idle, the value indicates the frequency
variation (burst frequency) of incoming requests.
The higher the value, the bigger the burst and the
longer the average response time at this
component. In contrast to this metric, the
average queue length does also include idle
periods when no requests are pending. If you
have 50% of the time just one outstanding
request, and the other 50% the SP is idle, the
average busy queue length will be 1. The average
queue length however, will be .
FAST Cache Dirty
Pages (%)
Advanced Only
Percentage of FAST Cache pages
owned by this SP that contain
data, which has not yet been
written back to disks.
This metric shows the instantaneous level of the
FAST Cache based on the last poll. It is not an
average over the entire polling interval.
FAST Cache MBs
Flushed (MB/s)
Advanced Only
Number of megabytes per second
that have been written from the
FAST Cache back to disks.
N/A
Characteristic Description Comment
Utilization Describes the fraction of a certain observation period
that the system component is busy serving incoming
requests. An SP or disk that shows 100% (or close to
100%) utilization is a system bottleneck since an
increase in the overall workload will not affect the
component throughput; the component has reached
its saturation point. Since a LUN is considered busy if
any of its disks is busy, LUN utilization usually
Since a RAID group can have
multiple partitions, the disks
utilization is a result of servicing
I/Os that belong to all LUNs
within this RAID group.
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presents a pessimistic view. That is, a high LUN
utilization value does not necessarily indicate that the
LUN is approaching its maximum capacity.
Queue Length The average number of requests within a certain time
interval waiting to be served by the component,
including the one in service.
A queue length of zero (which is
average) indicates an idle disk.
If three requests arrive at an
idle disk at the same time, only
one of them can be served
immediately; the other two
must wait in the queue,
resulting in a queue length of
three.
Response Time
(ms)
The average time, in milliseconds, required for one
request to pass through a system component,
including its waiting time.
The higher the queue length for
the disk, the more requests are
waiting in its queue, thus
increasing the average response
time of a single request. For a
given workload, queue length
and response time are directly
proportional.
Total Bandwidth
(MB/s)
The average amount of data in Mbytes that is passed
through a system component per second. Total
bandwidth includes both read and write requests.
Larger requests result usually in
a higher total bandwidth than
smaller requests.
Total
Throughput
(IO/s)
The average number of requests that pass through a
system component per second. Total throughput
includes both read and write requests.
Since smaller requests need
less processing time, they
usually result in a higher total
throughput than larger
requests.
Read Bandwidth
(MB/s)
The average number of Mbytes read that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
ones.
Read Size (KB) The average read request size in Kbytes. This number indicates whether
the read workload is oriented
more toward throughput (I/Os
per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an
IO Size Distribution chart.
Read
Throughput
(IO/s)
The average number of read requests passed through
a component per second.
Since smaller requests need
less processing time, they
usually result in a higher write
throughput than larger
requests.
Write
Bandwidth
(MB/s)
The average number of Mbytes written that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
ones.
Write Size (KB) The average write request size in Kbytes. This
number indicates whether the read workload is
oriented more toward throughput (I/Os per second)
or bandwidth (Mbytes/second). For a finer distinction
of I/O sizes, use an IO Size Distribution chart.
Sequential writes can get
coalesced in the write cache and
might result in larger disk
requests when flushed to disks.
Write
Throughput
(IO/s)
The average number of write requests passed
through a component per second.
Since smaller requests need
less processing time, they
usually result in a higher write
throughput than larger
requests.
Average Seek
Distance (GB)
Average seek distance in gigabytes. Longer seek distances result in
longer seek times and therefore
higher response times.
Defragmentation might help to
reduce seek distances.
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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
LUN
A LUN is an abstract object whose performance depends on various factors. The main aspect is whether a
host I/O can get satisfied by the cache or not. A cache hit does not require any disk access; a cache miss
however requires one or more disk accesses to complete the data request. Most cache statistics are
available only for the LUN object.
Unisphere Analyzer reports performance statistics for the following types of LUNs: regular host LUNs,
metaLUNs, thin LUNs, thick pool LUNs, and component LUNs, which are the underlying LUNs of a metaLUN.
Basic Characteristics
Service Time
(ms)
Time, in milliseconds, a request spent being serviced
by a component. It does not include time waiting in a
queue. Service time is mainly a characteristic of the
system component. However, larger I/Os take longer
and therefore usually result in lower throughput
(IO/s) but better bandwidth (Mbytes/s).
If there are at least three
outstanding requests to the
disk, it will optimize the order of
execution based on their locality
which can result in a shorter
service time.
Characteristic Description Comment
Average Busy
Queue Length
Advanced Only
Average number of
requests waiting at a
busy system
component to be
serviced, including the
request that is
currently in service.
Since this queue length is counted only when the disk is not
idle, the value indicates the frequency variation (burst
frequency) of incoming requests. The higher the value, the
bigger the burst and the longer the average response time at
this component. In contrast to this metric, the average queue
length does also include idle periods when no requests are
pending. If you have 50% of the time just one outstanding
request, and the other 50% the disk is idle, the average busy
queue length will be 1. The average queue length however,
will be .
Average Seek
Distance (GB)
Advanced Only
Average seek distance
in gigabytes.
Longer seek distances result in longer seek times and
therefore higher response times. Defragmentation might help
to reduce seek distances.
Characteristic Description Comment
Utilization Describes the fraction of a certain observation
period that the system component is busy
serving incoming requests. An SP or disk that
shows 100% (or close to 100%) utilization is a
system bottleneck since an increase in the
overall workload will not affect the component
throughput; the component has reached its
saturation point. Since a LUN is considered busy
if any of its disks is busy, LUN utilization usually
presents a pessimistic view. That is, a high LUN
utilization value does not necessarily indicate
that the LUN is approaching its maximum
capacity.
When the LUN becomes the
bottleneck, the utilization will be at
or close to 100%. However, since
I/Os can get serviced by multiple
disks an increase in workload might
still result in a higher throughput.
Queue Length The average number of requests within a certain
time interval waiting to be served by the
component, including the one in service.
A queue length of zero (which is
average) indicates an idle LUN.
Since there can be idle times during
the observed time period, the
average queue length can also be
smaller than 1. If you want to know
the average number of outstanding
requests when the LUN is busy, look
at the average busy queue length.
Response Time
(ms)
The average time, in milliseconds, required for
one request to pass through a system
component, including its waiting time.
The higher the queue length for a
LUN, the more requests are waiting
in its queue, thus increasing the
average response time of a single
request. For a given workload,
queue length and response time are
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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
directly proportional.
Total
Bandwidth
(MB/s)
The average amount of data in Mbytes that is
passed through a system component per second.
Total bandwidth includes both read and write
requests.
Larger requests usually result in a
higher total bandwidth than smaller
requests.
Total
Throughput
(IO/s)
The average number of requests that pass
through a system component per second. Total
throughput includes both read and write
requests.
Since smaller requests need a
shorter time for this, they usually
result in a higher total throughput
than larger requests.
Read
Bandwidth
(MB/s)
The average number of Mbytes read that were
passed through a component per second.
Larger requests usually result in a
higher bandwidth than smaller
requests.
Read Size (KB) The average read request size in Kbytes. This number indicates whether the
overall read workload is oriented
more toward throughput (I/Os per
second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for this LUN.
Read
Throughput
(IO/s)
The average number of read requests passed
through a component per second.
Since smaller requests need less
processing time, they usually result
in a higher read throughput than
larger requests.
Write
Bandwidth
(MB/s)
The average number of Mbytes written that were
passed through a component per second.
Larger requests usually result in a
higher bandwidth than smaller
requests.
Write Size (KB) The average write request size in Kbytes. This number indicates whether the
overall write workload is oriented
more toward throughput (I/Os per
second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the LUNs.
Write
Throughput
(IO/s)
The average number of write requests passed
through a component per second.
Since smaller requests need less
processing time, they usually result
in a higher write throughput than
larger requests.
Service Time
(ms)
Time, in milliseconds, a request spent being
serviced by a component. It does not include
time waiting in a queue. Service time is mainly a
characteristic of the system component.
However, larger I/Os take longer and therefore
usually result in lower throughput (IO/s) but
better bandwidth (Mbytes/s).
Larger requests usually have a
longer service time than smaller
requests.
Characteristic Description Comment
Full Stripe
Writes/s
Advanced
Average number of writes
requests per second that spanned
a whole stripe (all disks in a LUN).
This metric is applicable only to LUNs that are part
of a RAID 5 or RAID 3 Group. For these RAID
types, full stripe writes are most efficient since
data and parity can be written out to the disks
without having to pre-read any old data or parity
first.
Prefetch
Bandwidth
(MB/s)
The amount of data per second
that has been prefetched for this
particular LUN.
The amount of prefetched data depends on the
prefetch settings for this LUN. It indicates the
sequentiality of the workload for this LUN.
Used Prefetches
(%) Advanced
The indication of prefetching
efficiency.
To improve read bandwidth, two consecutive
requests trigger prefetching, thereby filling the
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Only read cache with data before it is requested. Thus,
sequential requests will receive the data from the
read cache instead of from the disks, which
results in a lower response time and higher
throughput. As the percentage of sequential
requests rises, so does the percentage of used
prefetches.
SP Cache Read
Hits/s Advanced
Only
The number of read requests that
were satisfied by either write or
read cache within a second.
An SP read cache hit occurs when recently
accessed data is re-referenced while it is still in
the cache.
SP Cache Read
Misses/s
Advanced Only
The rate of read requests that
could not be satisfied by the SP
cache and therefore required a
disk access.
SP Cache Reads
From WC/s
Average number of read requests
per second that were satisfied by
the write cache only.
Reads from write cache occur when recently
written data is read again while it is still in the
write cache. This is a subset of SP cache read hits
which includes requests satisfied by either the
write or the read cache.
SP Cache Reads
From RC/s
Average number of read requests
per second that were satisfied by
the read cache only.
Reads from read cache occur when data that has
been recently read or prefetched is re-read while
it is still in the read cache. This is a subset of SP
cache read hits which includes requests satisfied
by either the write or the read cache.
SP Cache Read
Hit Ratio
Advanced Only
The fraction of read requests
served from both read and write
caches vs. the number of read
requests to this LUN.
A higher ratio indicates better read performance.
SP Cache Write
Rehits/s
Advanced Only
The number of write requests per
second that were satisfied by the
write cache since they have been
referenced before and not yet
flushed to the disks.
SP cache write rehits occur when recently
accessed data is referenced again while it is still in
the write cache. This is a subset of SP Cache
Write Hits.
SP Cache Write
Hit Ratio
Advanced Only
The fraction of write requests that
were satisfied by the write cache
without requiring any disk access,
compared to the total number of
write requests to this LUN.
A higher ratio indicates better write performance.
SP Cache Write
Rehit Ratio
Advanced Only
The fraction of write requests that
were satisfied by the write cache
since they have been referenced
before and not yet flushed to the
disks, compared to the total
number of write requests to this
LUN.
This is a measure of how often the write cache
succeeded in eliminating a write operation to disk.
While improving the rehit ratio is useful it is more
beneficial to reduce the number of forced flushes.
SP Cache Write
Hits/s Advanced
Only
The number of write requests that
were satisfied by the write cache
without requiring any disk access.
SP cache write hits are either
requests that have been
referenced before and not yet
flushed to the disks (rehits) or
new write requests that did not
trigger any forced flushes.
Write requests that are not SP cache write hits are
referred to as SP cache write misses.
SP Cache Write
Misses/s
Advanced Only
The number of write requests per
second that could not be satisfied
by the write cache only, but also
required additional disk access.
Examples of SP cache write misses are write
requests that bypass the write cache due to their
size and write requests that trigger forced flushes.
SP Cache Forced
Flushes/ s
Advanced Only
Number of times per second the
cache had to flush pages to disk
to free space for incoming write
SP cache forced flushes are a measure of how
often write requests will have to wait for disk I/O
rather than be satisfied by an empty slot in the
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requests. SP cache forced flushes
indicate that the incoming
workload is higher than the back
end workload. A relatively high
number over a long period of time
suggests that you spread the load
over more disks.
write cache. In most well performing systems this
should be zero most of the time.
Disk Crossing
(%) Advanced
Only Percentage of requests that
require I/O to at least two disks
compared to the total number of
server requests.
A single disk crossing can involve more than two
disk drives; that is, more than two stripe element
crossings. Disk crossings relate to the LUN stripe
element size. Generally, a low value is needed for
good performance.
Average Busy
Queue Length
Advanced Only
Average number of requests
waiting at a busy system
component to be serviced,
including the request that is
currently in service.
Since this queue length is counted only when the
LUN is not idle, the value indicates the frequency
variation (burst frequency) of incoming requests.
The higher the value, the bigger the burst and the
longer the average response time at this
component. In contrast to this metric, the
average queue length does also include idle
periods when no requests are pending. If you
have 50%of the time just one outstanding
request, and the other 50% the LUN is idle, the
average busy queue length will be 1. The average
queue length however, will be .
Explicit Trespass
Count
The result of an external
command that you or the failover
software issue. When an SP
receives this command (from the
failover software or you issuing
the LUN trespass in Unisphere),
LUN ownership is transferred to
that SP.
This host-side performance characteristic is
displayed in both archive dump files and charts
(runtime and archive).
Implicit Trespass
Count
The result of software controls
within the storage system. An
example of an implicit trespass
operation is when LUN ownership
is transferred to the SP (non-
optimal paths) that receives the
heaviest I/O activity. Once a
threshold of I/Os is reached on
the non-optimal paths, the
CLARiiON implicitly trespasses the
LUN to that SP.
This host-side performance characteristic is
displayed in both archive dump files and charts
(runtime and archive).
FAST Cache
Read Hit/s
Advanced Only
Average number of read requests
per second for this LUN that were
satisfied by FAST Cache.
A FAST Cache read hit occurs when data is read,
which is currently present in FAST Cache. This
includes data that has been flushed already, but
not yet invalidated in the FAST Cache.
FAST Cache
Read Misses/s
Advanced Only
Average number of read requests
per second for this LUN that were
not satisfied by FAST Cache.
A FAST Cache read miss does not necessarily
require disk access. It still might get satisfied by
the SP cache.
FAST Cache
Read Hit Ratio
Advanced Only
The fraction of all read requests
for this LUN that have been
satisfied by FAST Cache.
Valid numbers are between 0 and 1.
FAST Cache
Write Hits/s
Advanced Only
Average number of write requests
per second for this LUN that were
satisfied by FAST Cache.
Write requests that are not write cache hits are
referred to as write cache misses.
FAST Cache
Write Misses/s
Advanced Only
Average number of write requests
per second for this LUN that were
not satisfied by FAST Cache.
A FAST Cache write miss does not necessarily
require a disk access. It still might get satisfied by
the SP cache.
FAST Cache
Write Hit Ratio
The fraction of all write requests
for this LUN that have been
N/A
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Optimal and Nonoptimal Characteristics (Advanced-only)
You will see the Optimal and Nonoptimal performance characteristics only if you enable the advanced mode
in the Customize dialog box and are running the active/active feature. Optimal refers to the path that is
ready to do I/O and will yield the best performance. Nonoptimal refers to the path that is ready to do I/O,
but may not yield the best performance. The following Optimal and Nonoptimal performance characteristics
apply to LUN objects:
Advanced-only Characteristics
MetaLUNs
Unisphere Analyzer reports the following performance statistics for metaLUNs:
Basic Characteristics
Advanced Only satisfied by FAST Cache.
Optimal
Performance
Characteristic
Nonoptimal
Performance
Characteristic
Utilization-Optimal [%] Utilization-Nonoptimal [%]
Queue Length-Optimal Queue Length-Nonoptimal
Response Time-Optimal Response Time-Nonoptimal
Total Bandwidth-Optimal [MB/s] Total Bandwidth-Nonoptimal [MB/s]
Total Throughput-Optimal [IO/s] Total Throughput-Nonoptimal [IO/s
Read Bandwidth-Optimal [MB/s] Read Bandwidth-Nonoptimal [MB/s]
Read Size-Optimal [KB] Read Size-Nonoptimal [KB]
Read Throughput-Optimal [IO/s] Read Throughput-Nonoptimal [IO/s]
Write Bandwidth-Optimal [MB/s] Write Bandwidth-Nonoptimal [MB/s]
Write Size-Optimal [KB] Write Size-Nonoptimal [KB]
Write Throughput-Optimal [IO/s] Write Throughput-Nonoptimal [IO/s]
Average Busy Queue Length-Optimal Average Busy Queue Length-Nonoptimal
Service Time-Optimal [ms] Service Time-Nonoptimal [ms]
Explicit Trespass Count-Optimal Explicit Trespass Count-Nonoptimal
Implicit Trespass Count-Optimal Implicit Trespass Count-Nonoptimal
Characteristic Description Comment
Utilization Describes the fraction of a certain observation
period that the system component is busy serving
incoming requests. An SP or disk that shows 100%
(or close to 100%) utilization is a system bottleneck
since an increase in the overall workload will not
affect the component throughput; the component
has reached its saturation point. Since a LUN is
considered busy if any of its disks is busy, LUN
utilization usually presents a pessimistic view. That
is, a high LUN utilization value does not necessarily
indicate that the LUN is approaching its maximum
capacity.
When the SP becomes the
bottleneck, the utilization will be
at or close to 100%. An increase
in workload will have no further
impact on the SP throughput, but
the I/O response time will start
increasing more aggressively.
Queue Length The average number of requests within a certain
time interval waiting to be served by the
component, including the one in service.
A queue length of zero (which is
average) indicates an idle
system. If three requests arrive
at an idle SP at the same time,
only one of them can be served
immediately; the other two must
wait in the queue, resulting in a
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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
queue length of three.
Response Time
(ms)
The average time, in milliseconds, required for one
request to pass through a system component,
including its waiting time.
The higher the queue length for
the SP, the more requests are
waiting in its queue, thus
increasing the average response
time of a single request. For a
given workload, queue length
and response time are directly
proportional.
Total
Bandwidth
(MB/s)
The average amount of data in Mbytes that is
passed through a system component per second.
Total bandwidth includes both read and write
requests.
Larger requests usually result in
a higher total bandwidth than
smaller requests.
Total
Throughput
(IO/s)
The average number of requests that pass through
a system component per second. Total throughput
includes both read and write requests.
Since smaller requests need a
shorter time for this, they usually
result in a higher total
throughput than larger requests.
Read
Bandwidth
(MB/s)
The average number of Mbytes read that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Read Size (KB) The average read request size in Kbytes. This number indicates whether
the overall read workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
Read
Throughput
(IO/s)
The average number of read requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher read
throughput than larger requests.
Write
Bandwidth
(MB/s)
The average number of Mbytes written that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Write Size (KB) The average write request size in Kbytes. This number indicates whether
the overall write workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
Write
Throughput
(IO/s)
The average number of write requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher write
throughput than larger requests.
Service Time
(ms)
Time, in milliseconds, a request spent being
serviced by a component. It does not include time
waiting in a queue. Service time is mainly a
characteristic of the system component. However,
larger I/Os take longer and therefore usually result
in lower throughput (IO/s) but better bandwidth
(Mbytes/s).
Larger requests usually have a
longer service time than smaller
requests.
Characteristic Description Comment
Full Stripe
Writes/s
Average number of writes
requests per second that spanned
This metric is applicable only to LUNs that are part
of a RAID 5 or RAID 3 Group. For these RAID
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Advanced a whole stripe (all disks in a LUN). types, full stripe writes are most efficient since
data and parity can be written out to the disks
without having to pre-read any old data or parity
first.
Used Prefetches
(%) Advanced
Only
The indication of prefetching
efficiency.
To improve read bandwidth, two consecutive
requests trigger prefetching, thereby filling the
read cache with data before it is requested. Thus,
sequential requests will receive the data from the
read cache instead of from the disks, which
results in a lower response time and higher
throughput. As the percentage of sequential
requests rises, so does the percentage of used
prefetches.
SP Cache Read
Hits/s Advanced
Only
The number of read requests that
were satisfied by either write or
read cache within a second.
An SP cache read hit occurs when recently
accessed data is re-referenced while it is still in
the cache.
SP Cache Read
Misses/s
Advanced Only
The rate of read requests that
could not be satisfied by the SP
cache and therefore required a
disk access.
SP Cache Reads
From WC/s
Average number of read requests
per second that were satisfied by
the write cache only.
SP cache reads from write occur when recently
written data is read again while it is still in the
write cache. This is a subset of SP cache read hits
which includes requests satisfied by either the
write or the read cache.
SP Cache Reads
From RC/s
Average number of read requests
per second that were satisfied by
the read cache only.
SP cache reads from read occur when data that
has been recently read or prefetched is re-read
while it is still in the read cache. This is a subset
of SP cache read hits, which includes requests
satisfied by either the write or the read cache.
SP Cache Read
Hit Ratio
Advanced Only
The fraction of read requests
served from both read and write
caches vs. the number of read
requests to this LUN.
A higher ratio indicates better read performance.
SP Cache Write
Rehits/s
Advanced Only
The number of write requests per
second that were satisfied by the
write cache since they have been
referenced before and not yet
flushed to the disks.
Write cache rehits occur when recently accessed
data is referenced again while it is still in the write
cache. This is a subset of Write Cache Hits.
SP Cache Write
Hit Ratio
Advanced Only
The fraction of write requests that
were satisfied by the write cache
without requiring any disk access,
compared to the total number of
write requests to this LUN.
A higher ratio indicates better write performance.
SP Cache Write
Rehit Ratio
Advanced Only
The fraction of write requests that
were satisfied by the write cache
since they have been referenced
before and not yet flushed to the
disks, compared to the total
number of write requests to this
LUN.
This is a measure of how often the write cache
succeeded in eliminating a write operation to disk.
While improving the rehit ratio is useful it is more
beneficial to reduce the number of forced flushes.
SP Cache Write
Hits/s Advanced
Only
The number of write requests that
were satisfied by the write cache
without requiring any disk access.
SP cache write hits are either
requests that have been
referenced before and not yet
flushed to the disks (rehits) or
new write requests that did not
trigger any forced flushes.
Write requests that are not SP cache write hits are
referred to as SP cache write misses.
SP Cache Write The number of write requests per Write requests that cause forced flushes or that
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Misses/s
Advanced Only
second that could not be satisfied
by the write cache only, but also
required additional disk access.
Examples of SP cache write
misses are write requests that
bypass the write cache due to
their size and write requests that
trigger forced flushes.
bypass the write cache due to their size are
examples of SP cache write misses.
SP Cache Forced
Flushes/s
Advanced Only
Number of times per second the
cache had to flush pages to disk
to free space for incoming write
requests. SP cache forced flushes
indicate that the incoming
workload is higher than the back
end workload. A relatively high
number over a long period of time
suggests that you spread the load
over more disks.
SP cache forced flushes are a measure of how
often write requests will have to wait for disk I/O
rather than be satisfied by an empty slot in the
write cache. In most well performing systems this
should be zero most of the time.
Disk Crossing
(%) Advanced
Only Percentage of requests that
require I/O to at least two disks
compared to the total number of
server requests.
A single disk crossing can involve more than two
disk drives; that is, more than two stripe element
crossings. Disk crossings relate to the LUN stripe
element size. Generally, a low value is needed for
good performance.
Average Busy
Queue Length
Advanced Only
Average number of requests
waiting at a busy system
component to be serviced,
including the request that is
currently in service.
Since this queue length is counted only when the
LUN is not idle, the value indicates the frequency
variation (burst frequency) of incoming requests.
The higher the value, the bigger the burst and the
longer the average response time at this
component. In contrast to this metric, the
average queue length does also include idle
periods when no requests are pending. If you
have 50%of the time just one outstanding
request, and the other 50% the LUN is idle, the
average busy queue length will be 1. The average
queue length however, will be .
LUN Read
Crossings/s
Advanced Only
The number of LUN crossings per
second that a read request to a
MetaLUN caused.
Since metaLUNs consist of multiple LUNs, a single
read request can access disk drives that belong to
two or more of these conventional LUNs.
LUN Write
Crossings/s
Advanced Only
The number of LUN crossings per
second that a write request to a
metaLUN caused.
Since metaLUNs consist of multiple LUNs, a single
write request can access disk drives that belong
to two or more of these conventional LUNs.
Explicit Trespass
Count
The result of an external
command that you or the failover
software issues. When an SP
receives this command (from the
failover software or you issuing
the LUN trespass in Unisphere),
LUN ownership is transferred to
that SP.
Host-side performance characteristic displayed in
both archive dump files and charts (runtime and
archive).
Implicit Trespass
Count
The result of software controls
within the storage system. An
example of an implicit trespass
operation is when LUN ownership
is transferred to the SP (non-
optimal paths) that receives the
heaviest I/O activity. Once a
threshold of I/Os is reached on
the non-optimal paths, the
CLARiiON implicitly trespasses the
LUN to that SP.
Host-side performance characteristic displayed in
both archive dump files and charts (runtime and
archive).
FAST Cache
Read Hit/s
Advanced Only
Average number of read requests
per second for this metaLUN that
were satisfied by FAST Cache.
A FAST Cache read hit occurs when data is read,
which is currently present in FAST Cache. This
includes data that has been flushed already, but
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Optimal and Nonoptimal Characteristics (Advanced-only)
You will see the Optimal and Nonoptimal performance characteristics only if you enable the advanced mode
in the Customize dialog box and are running the active/active feature. Optimal refers to the path that is
ready to do I/O and will yield the best performance. Nonoptimal refers to the path that is ready to do I/O,
but may not yield the best performance. The following Optimal and Nonoptimal performance characteristics
apply to MetaLUN objects:
Advanced-only Characteristics
Thin LUNs
Unisphere Analyzer reports the following performance statistics for thin LUNs:
Basic Characteristics
not yet invalidated in the FAST Cache.
FAST Cache
Read Misses/s
Advanced Only
Average number of read requests
per second for this metaLUN that
were not satisfied by FAST Cache.
A FAST Cache read miss does not necessarily
require disk access. It still might get satisfied by
the SP cache.
FAST Cache
Read Hit Ratio
Advanced Only
The fraction of all read requests
for this metaLUN that have been
satisfied by FAST Cache.
Valid numbers are between 0 and 1.
FAST Cache
Write Hits/s
Advanced Only
Average number of write requests
per second for this metaLUN that
were satisfied by FAST Cache.
Write requests that are not SP cache write hits are
referred to as SP cache write misses.
FAST Cache
Write Misses/s
Advanced Only
Average number of write requests
per second for this metaLUN that
were not satisfied by FAST Cache.
A FAST Cache write miss does not necessarily
require a disk access. It still might get satisfied by
the SP cache.
FAST Cache
Write Hit Ratio
Advanced Only
The fraction of all write requests
for this metaLUN that have been
satisfied by FAST Cache.
N/A
Optimal
Performance
Characteristic
Nonoptimal
Performance
Characteristic
Utilization-Optimal [%] Utilization-Nonoptimal [%]
Queue Length-Optimal Queue Length-Nonoptimal
Response Time-Optimal Response Time-Nonoptimal
Total Bandwidth-Optimal [MB/s] Total Bandwidth-Nonoptimal [MB/s]
Total Throughput-Optimal [IO/s] Total Throughput-Nonoptimal [IO/s
Read Bandwidth-Optimal [MB/s] Read Bandwidth-Nonoptimal [MB/s]
Read Size-Optimal [KB] Read Size-Nonoptimal [KB]
Read Throughput-Optimal [IO/s] Read Throughput-Nonoptimal [IO/s]
Write Bandwidth-Optimal [MB/s] Write Bandwidth-Nonoptimal [MB/s]
Write Size-Optimal [KB] Write Size-Nonoptimal [KB]
Write Throughput-Optimal [IO/s] Write Throughput-Nonoptimal [IO/s]
Average Busy Queue Length-Optimal Average Busy Queue Length-Nonoptimal
Service Time-Optimal [ms] Service Time-Nonoptimal [ms]
Explicit Trespass Count-Optimal Explicit Trespass Count-Nonoptimal
Implicit Trespass Count-Optimal Implicit Trespass Count-Nonoptimal
Characteristic Description Comment
Utilization Describes the fraction of a certain observation When the SP becomes the
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period that the system component is busy serving
incoming requests. An SP or disk that shows 100%
(or close to 100%) utilization is a system bottleneck
since an increase in the overall workload will not
affect the component throughput; the component
has reached its saturation point. Since a LUN is
considered busy if any of its disks is busy, LUN
utilization usually presents a pessimistic view. That
is, a high LUN utilization value does not necessarily
indicate that the LUN is approaching its maximum
capacity.
bottleneck, the utilization will be
at or close to 100%. An increase
in workload will have no further
impact on the SP throughput, but
the I/O response time will start
increasing more aggressively.
Queue Length The average number of requests within a certain
time interval waiting to be served by the
component, including the one in service.
A queue length of zero (which is
average) indicates an idle
system. If three requests arrive
at an idle SP at the same time,
only one of them can be served
immediately; the other two must
wait in the queue, resulting in a
queue length of three.
Response Time
(ms)
The average time, in milliseconds, required for one
request to pass through a system component,
including its waiting time.
The higher the queue length for
the SP, the more requests are
waiting in its queue, thus
increasing the average response
time of a single request. For a
given workload, queue length
and response time are directly
proportional.
Total
Bandwidth
(MB/s)
The average amount of data in Mbytes that is
passed through a system component per second.
Total bandwidth includes both read and write
requests.
Larger requests usually result in
a higher total bandwidth than
smaller requests.
Total
Throughput
(IO/s)
The average number of requests that pass through
a system component per second. Total throughput
includes both read and write requests.
Since smaller requests need a
shorter time for this, they usually
result in a higher total
throughput than larger requests.
Read
Bandwidth
(MB/s)
The average number of Mbytes read that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Read Size (KB) The average read request size in Kbytes. This number indicates whether
the overall read workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
Read
Throughput
(IO/s)
The average number of read requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher read
throughput than larger requests.
Write
Bandwidth
(MB/s)
The average number of Mbytes written that were
passed through a component per second.
Larger requests usually result in
a higher bandwidth than smaller
requests.
Write Size (KB) The average write request size in Kbytes. This number indicates whether
the overall write workload is
oriented more toward throughput
(I/Os per second) or bandwidth
(Mbytes/second). For a finer
distinction of I/O sizes, use an IO
Size Distribution chart for the
LUNs.
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Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
Optimal and Nonoptimal Characteristics (Advanced-only)
You will see the Optimal and Nonoptimal performance characteristics only if you enable the advanced mode
in the Customize dialog box and are running the active/active feature. Optimal refers to the path that is
ready to do I/O and will yield the best performance. Nonoptimal refers to the path that is ready to do I/O,
but may not yield the best performance. The following Optimal and Nonoptimal performance characteristics
apply to thin LUN objects:
Advanced-only Characteristics
Pools
Unisphere Analyzer reports the following performance statistics for pools:
Advanced-only Characteristics
Write
Throughput
(IO/s)
The average number of write requests passed
through a component per second.
Since smaller requests need less
processing time, they usually
result in a higher write
throughput than larger requests.
Service Time
(ms)
Time, in milliseconds, a request spent being
serviced by a component. It does not include time
waiting in a queue. Service time is mainly a
characteristic of the system component. However,
larger I/Os take longer and therefore usually result
in lower throughput (IO/s) but better bandwidth
(Mbytes/s).
Since thin LUNs consist of
multiple LUNs, a single read
request can access disk drives
that belong to two or more of
these conventional LUNs.
Characteristic Description Comment
Average Busy
Queue Length
Advanced Only
Average number of
requests waiting at a
busy system
component to be
serviced, including the
request that is
currently in service.
Since this queue length is counted only when the LUN is not
idle, the value indicates the frequency variation (burst
frequency) of incoming requests. The higher the value, the
bigger the burst and the longer the average response time
at this component. In contrast to this metric, the average
queue length does also include idle periods when no
requests are pending. If you have 50%of the time just one
outstanding request, and the other 50% the LUN is idle, the
average busy queue length will be 1. The average queue
length however, will be .
Optimal
Performance
Characteristic
Nonoptimal
Performance
Characteristic
Utilization-Optimal [%] Utilization-Nonoptimal [%]
Queue Length-Optimal Queue Length-Nonoptimal
Response Time-Optimal Response Time-Nonoptimal
Total Bandwidth-Optimal [MB/s] Total Bandwidth-Nonoptimal [MB/s]
Total Throughput-Optimal [IO/s] Total Throughput-Nonoptimal [IO/s
Read Bandwidth-Optimal [MB/s] Read Bandwidth-Nonoptimal [MB/s]
Read Size-Optimal [KB] Read Size-Nonoptimal [KB]
Read Throughput-Optimal [IO/s] Read Throughput-Nonoptimal [IO/s]
Write Bandwidth-Optimal [MB/s] Write Bandwidth-Nonoptimal [MB/s]
Write Size-Optimal [KB] Write Size-Nonoptimal [KB]
Write Throughput-Optimal [IO/s] Write Throughput-Nonoptimal [IO/s]
Average Busy Queue Length-Optimal Average Busy Queue Length-Nonoptimal
Service Time-Optimal [ms] Service Time-Nonoptimal [ms]
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MirrorView/A
When using the optional replication software, Mirrorview/A (asynchronous mirroring), changed data is
copied from a primary image, the source LUN, to a secondary image. These updates can be invoked either
automatically or manually. Either way, there will be times when primary and secondary image are different,
that is, out of sync. Unisphere Analyzer provides performance statistics regarding the data transfer and the
difference between the primary and secondary images for each Remote Mirror.
Basic Characteristics
Characteristic Description Comment
FAST Cache Read
Hits/s Advanced Only
Average number of read
requests per second for this
pool that were satisfied by
FAST Cache.
A FAST Cache read hit occurs when data is read,
which is currently present in FAST Cache. This
includes data that has been flushed already, but
not yet invalidated in the FAST Cache.
FAST Cache Read
Misses/s Advanced
Only
Average number of read
requests per second for this
pool that were not satisfied by
FAST Cache.
A FAST Cache read miss does not necessarily
require a disk access. It still might get statisfied
by the SP cache.
FAST Cache Read Hit
Ratio Advanced Only
The fraction of all read
requests for this pool that have
been satisfied by FAST Cache.
Valid numbers are between 0 and 1.
FAST Cache Read
Write Hits/s
Advanced Only
Average number of write
requests per second for this
pool that were satisfied by
FAST Cache.
Write requests that are not write cache hits are
referred to as write cache misses.
FAST Cache Write
Misses/s Advanced
Only
Average number of write
requests per second for this
pool that were not satisfied by
FAST Cache.
A FAST Cache write miss does not necessarily
require a disk access. It still might get satisfied
by the SP cache.
FAST Cache Write Hit
Ratio Advanced Only
The fraction of all write
requests for this LUN that have
been satisfied by FAST Cache.
N/A
Characteristic Description Comment
Total Bandwidth
(MB/s)
Bandwidth of the update
transfers from the
primary image to the
secondary image(s).
Total Throughput
(IO/s)
Throughput of the update
transfers from the
primary image to the
secondary image(s).
Average Transfer
Size (KB)
Average size of update
transfers from the
primary image to the
secondary image(s).
Time Lag (min) The measure of how far,
in time, the secondary
image is behind the
primary image(s).
This is the time that has passed since the last update
successfully finished.
Megabyte Lag
(MB)
The number of
megabytes by which the
secondary image differs
from the primary image
(s).
This number indicates how much data has to be written to
the secondary image to make both, primary and
secondary image in-sync. During an update, this value is a
combination of how much data is remaining to be sent plus
any newly updated data that will be part of the following
update.
Cycle Count The number of updates
that completed during the
polling interval.
An update that started but did not finish within the same
polling interval will not be counted. This number will be
greater than one only if the time between polls is fairly
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SnapSession
The snapshot characteristics apply to a Snapshot Session node only (SnapView software required). In the
Snapshot Session, these characteristics are shown as SS.
SnapSessions are available with the optional software package, SnapView. During a SnapSession, data that
a production host overwrites on a source LUN will be saved in the SnapCache (part of the Reserved LUN
Pool), thus preserving a point-in-time view of this LUN from the time the SnapSession was created (Start
Session). This view can then get exported to another host (Activate Session) that needs to access this data.
The following table contains all statistics that Unisphere Analyzer provides for a SnapSession. Since a
SnapSession can contain multiple SnapShot Source LUNs, the statistics comprise all LUNs that are
associated with this SnapSession.
Basic Characteristics
Advanced-only Characteristics (Advanced Characteristics also include the Basic ones)
Ports
Unisphere Analyzer reports performance statistics for front-end ports.
Advanced-only Characteristics
large.
Average Cycle
Time (min)
The average duration of
all updates that finished
within the polling
interval..
If only a single update finished within the polling interval
(Cycle Count = 1), this time indicates the duration of this
update. For multiple update completions (Cycle Count >
1), this value will return their average duration.
Characteristic Description Comment
Reads From
Snapshot LUN
The number of read requests on
snapshots during this snapshot session.
These are requests that originate for
instance from a backup host and read data
either from the source LUN or the
SnapCache.
Reads From
Snapshot Source
LUN
The number of reads during this
Snapshot session from the source LUN.
It is calculated by the difference
between Total Reads in Session and
Reads From Cache.
These are read requests that originate from
a backup host and access data that has not
been overwritten since the SnapSession
started and therefore are satisfied by the
Source LUN.
Writes To
Snapshot Source
LUN
The number of writes during this
Snapshot session to the source LUN (on
the pertinent SP).
Characteristic Description Comment
Reads From
Snapshot Cache
Advanced Only
The number of reads during this
session that have resulted in a
read from the Snapshot cache
(instead of a read from the source
LUN).
These are read requests that originate from a
backup host and access data that has been
previously overwritten on the source LUN
during this SnapSession and therefore are
satisfied by one or more Snap Cache LUNs.
Writes To Snapshot
Cache Advanced Only
The number of writes to the
source LUN this session that
triggered a copy-on-write
operation (the first write to each
snapshot cache chunk region).
Write requests that trigger multiple copy-on-
first-write operations due to misalignment or
their size will only be counted once.
Writes Larger Than
Cache Chunk Size
Advanced Only
The number of writes to the
source LUN during this session
that were larger than the chunk
size (they have resulted in
multiple writes to the cache).
These writes result in multiple copy-on-first-
write operations.
Chunks Used in
Snapshot Copy
Session Advanced
Only
The number of snapshot cache
chunks that this session has used.
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Highlight a performance metric
Expand and Collapse
Select or Highlight
Checkbox
IO Size Distribution Detail chart
IO Size Distribution Summary Chart
LUN IO Disk Detail chart
Performance Detail chart
Performance Overview window
Performance Summary chart
Performance Survey chart
Data Logging
Customize dialog box - General
Customize dialog - Archives
Customize dialog - Fonts
Customize dialog - Line Charts
Customize dialog - Summary Charts
Customize dialog - Survey Charts
Customize dialog - Warnings
Control Panel - Policies tab
Policy Builder
Object states
Operational states
Display an archive file
Display a real-time chart
Customize Analyzer displays
Retrieve Performance Data and Store it in an Archive File
Configure a Performance Detail chart
Display a Performance Detail chart
Display a Performance Summary chart
Display a Performance Survey chart
Display an IO Size Distribution chart
Display a LUN IO Disk Detail chart
Display storage system performance information
Dump archive files into text format
Characteristic Description Comment
Queue Full
Count
The number of Queue Full events
that occurred for a particular
front-end port during a polling
interval.
A Queue Full response is sent to the host when the
port receives more requests than it can accept at
once. This event should never occur in a properly
configured SAN environment.
Related references
Related tasks
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Create a policy
Destroy a policy
Measure a policy
Modify a policy
Run a policy
Stop the current policy
About Unisphere Analyzer
Analyzer dependencies
Analyzer charts (real time and archive file)
Workload characteristics
Use Analyzer to monitor cache performance
About policies
Work with the Policy Builder wizard
Related concepts
Pgina 19 de 19Performance Characteristics
07/05/2015http://10.128.29.118/help/en_US/integrated/vnxuni_c_analyzer_performance_charact...