Fundamentals ASM
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Session id: 40288
Automatic Storage ManagementAutomatic Storage ManagementThe New Best PracticeThe New Best Practice
Steve AdamsIxora
Rich LongOracle Corporation
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The Challenge
Todays databases
large
growing
Storage requirements
acceptable performance
expandable and scalable
high availability low maintenance
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Outline
Introduction
get excited about ASM
Current best practices
complex, demanding, but achievable
Automatic storage management
simple, easy, better
Conclusion
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Current Best Practices
General principles to follow
direct I/O
asynchronous I/O
striping
mirroring
load balancing
Reduced expertise and analysis required avoids all the worst mistakes
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Buffered I/O
File
System
Cache
Database Cache
SGA
PGA
Reads
stat: physical reads read from cache
may requirephysical read
Writes
written to cache
synchronously
(Oracle waits untilthe data is safely ondisk too)
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Direct I/O
File
System
Cache
I/O
bypasses filesystem cache
Memory
file system cachedoes not containdatabase blocks(so its smaller)
database cachecan be larger
Database Cache
SGA
PGA
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Buffered I/O Cache Usage
Database Cache
File
System
Cache
Legend:
hot datarecent warm data
older warm data
recent cold data
o/s data
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Direct I/O Cache Usage
Database Cache
Legend:
hot datarecent warm data
older warm data
recent cold data
o/s data
File
System
Cache
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Cache Effectiveness
Buffered I/O
overlap wastes memory caches single use data
simple LRU policy
file system cache hitsare relatively expensive
extra physical read andwrite overheads
floods file systemcache with Oracle data
Direct I/O
no overlap no single use data
segmented LRU policy
all cached data is foundin the database cache
no physical I/Ooverheads
non-Oracle datacached more effectively
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Buffered Log Writes
File
System
Cache
Log BufferSGA Most redo log writes
address part of a filesystem block
File system reads the
target block first then copies the data
Oracle waits for both
the read and the write a full disk rotation is
needed in between
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I/O Efficiency
Buffered I/O
small writes must wait for
preliminary read
large reads & writes
performed as aseries of singleblock operations
tablespace block sizemust match file systemblock size exactly
Direct I/O
small writes no need to re-write
adjacent data
large reads & writes
passed down thestack without anyfragmentation
may use anytablespace block sizewithout penalty
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Direct I/O How To
May need to
set filesystemio_optionsparameter set file system mount options
configure using operating system commands
Depends on
operating system platform
file system type
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Synchronous I/O
Processes wait for I/O
completion and results A process can only use
one disk at a time
For a series of I/Os tothe same disk
the hardware cannotservice the requests inthe optimal order
scheduling latencies
DBWn write batch
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Asynchronous I/O
Can perform other tasks
while waiting for I/O Can use many disks at
once
For a batch of I/Os tothe same disk
the hardware canservice the requests inthe optimal order
no scheduling latencies
DBWn write batch
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Asynchronous I/O How To
Threaded asynchronous I/O simulation
multiple threads perform synchronous I/O high CPU cost if intensively used
only available on some platforms
Kernelized asynchronous I/O
must use raw devicesor a pseudo device driver product
eg: Veritas Quick I/O, Oracle Disk Manager, etc
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Striping Benefits
Concurrency
hot spots are spread over multiple disks whichcan service concurrent requests in parallel
Transfer rate
large reads & writes use multiple disk in parallel
I/O spread
full utilization of hardware investment important for systems relatively few large disks
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Striping Fine or Coarse
Concurrency coarse grain
most I/Os should be serviced by a single disk caching ensures that disk hot spots are not small
1 Mb is a reasonable stripe element size
Transfer rate fine grain
large I/Os should be serviced by multiple disks
but very fine striping increases rotational latencyand reduces concurrency
128 Kb is commonly optimal
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Striping Breadth
Comprehensive (SAME)
all disks in one stripe ensures even utilization
of all disks
needs reconfiguration
to increase capacity
without a disk cachelog write performancemay be unacceptable
Broad (SAME sets)
two or more stripe sets one sets may be busy
while another is idle
can increase capacity
by adding a new set
can use a separate diskset to isolate log filesfrom I/O interference
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Striping How To
Stripe breadth
broad (SAME sets) to allow for growth
to isolate log file I/O
comprehensive (SAME) otherwise
Stripe grain
choose coarse for high concurrency applications
choose fine for low concurrency applications
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Data Protection
Mirroring
only half the raw diskcapacity is usable
can read from eitherside of the mirror
must write to bothsides of the mirror
Half the data capacity
Maximum I/O capacity
RAID-5
parity data use thecapacity of one disk
only one image fromwhich to read
must read and writeboth the data and parity
Nearly full data capacity
Less than half I/O ability
Data capacity is much cheaper than I/O capacity.
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Mirroring Software or Hardware
Software mirroring
a crash can leave mirrors inconsistent complete resilvering takes too long
so a dirty region logis normally needed
enumerates potentially inconsistent regions
makes resilvering much faster
but it is a major performance overhead
Hardware mirroring is best practice
hot spare disksshould be maintained
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Data Protection How To
Choose mirroring, not RAID-5
disk capacity is cheap I/O capacity is expensive
Use hardware mirroring if possible
avoid dirty region logging overheads
Keep hot spares
to re-establish mirroring quickly after a failure
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Load Balancing Triggers
Performance tuning
poor I/O performance adequate I/O capacity
uneven workload
Workload growth
inadequate I/O capacity
new disks purchased
workload must beredistributed
Data growth
data growth requiresmore disk capacity
placing the new data onthe new disks would
introduce a hot spot
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Load Balancing Reactive
Approach
monitor I/O patterns and densities move files to spread the load out evenly
Difficulties
workload patterns may vary
file sizes may differ, thus preventing swapping
stripe sets may have different I/O characteristics
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Load Balancing How To
Be prepared
choose a small, fixed datafile size use multiple such datafiles for each tablespace
distribute these datafiles evenly over stripe sets
When adding capacity
for each tablespace, move datafiles pro-rata fromthe existing stripe sets into the new one
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Automatic Storage Management
What is ASM?
Disk Groups Dynamic Rebalancing
ASM Architecture ASM Mirroring
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Automatic Storage Management
New capability in the Oracle database kernel
Provides a vertical integration of the file system andvolume manager for simplified management ofdatabase files
Spreads database files across all available storage foroptimal performance
Enables simple and non-intrusive resource allocation
with automatic rebalancing Virtualizes storage resources
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ASM Disk Groups
A pool of disks managed as alogical unit
Disk Group
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ASM Disk Groups
A pool of disks managed as alogical unit
Partitions total disk space intouniform sized megabyte units
Disk Group
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ASM Disk Groups
A pool of disks managed as alogical unit
Partitions total disk space intouniform sized megabyte units
ASM spreads each file evenly
across all disks in a diskgroup
Disk Group
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ASM Disk Groups
A pool of disks managed as alogical unit
Partitions total disk space intouniform sized megabyte units
ASM spreads each file evenly
across all disks in a diskgroup
Coarse or fine grain striping
based on file type
Disk Group
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ASM Disk Groups
A pool of disks managed as alogical unit
Partitions total disk space intouniform sized megabyte units
ASM spreads each file evenlyacross all disks in a diskgroup
Coarse or fine grain stripingbased on file type
Disk groups integrated withOracle Managed Files
Disk Group
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes
Disk Group
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Only move data proportional
to storage added
Disk Group
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Only move data proportional
to storage added
No need for manual I/O tuning
Disk Group
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Online migration to new
storage
Disk Group
ASM D i R b l i
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Online migration to new
storage
Disk Group
ASM D i R b l i
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Online migration to new
storage
Disk Group
ASM D i R b l i
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ASM Dynamic Rebalancing
Automatic online rebalancewhenever storage
configuration changes Online migration to new
storage
Disk Group
ASM A hit t
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ASM Architecture
Pool of Storage
ASM Instance
NonRAC
Database
Server
Oracle
DB Instance
Disk Group
ASM A hit t
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ASM Architecture
ClusteredPool of Storage
ASM Instance ASM Instance
RAC
Database
ClusteredServers
Oracle
DB Instance
Oracle
DB Instance
Disk Group
ASM Architect re
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ASM Architecture
ClusteredPool of Storage
ASM Instance ASM Instance
RAC
Database
ClusteredServers
Oracle
DB Instance
Oracle
DB Instance
Disk GroupDisk Group
ASM Architecture
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ASM Architecture
ClusteredPool of Storage
ASM InstanceASM Instance ASM Instance ASM Instance
RAC orNonRAC
Databases
ClusteredServers
Oracle
DB Instance
Oracle
DB Instance
Oracle
DB Instance
Oracle
DB Instance
Oracle
DB Instance
Disk GroupDisk Group
ASM Mirroring
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ASM Mirroring
3 choices for disk group redundancy
External: defers to hardware mirroring Normal: 2-way mirroring
High: 3-way mirroring
Integration with database removes need fordirty region logging
ASM Mirroring
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ASM Mirroring
Mirror at extent level
Mix primary & mirror extents on each disk
ASM Mirroring
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ASM Mirroring
Mirror at extent level
Mix primary & mirror extents on each disk
ASM Mirroring
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ASM Mirroring
No hot spare disk required
Just spare capacity
Failed disk load spread among survivors
Maintains balanced I/O load
Conclusion
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Conclusion
Best practice is built into ASM
ASM is easy ASM benefits
performance
availability
automation
Best Practice Is Built Into ASM
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Best Practice Is Built Into ASM
I/O to ASM files is direct, not buffered
ASM allows kernelized asynchronous I/O ASM spreads the I/O as broadly as possible
can have both fine and coarse grain striping
ASM can provide software mirroring does not require dirty region logging
does not require hot spares, just spare capacity
When new disks are added ASM does loadbalancing automatically without downtime
ASM is Easy
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ASM is Easy
You only need to answer two questions
Do you need a separate log file disk group? intensive OLTP application with no disk cache
Do you need ASM mirroring?
storage not mirrored by the hardware
ASM will do everything else automatically
Storage management is entirely automated
using BIGFILE tablespaces, you need nevername or refer to a datafile again
ASM Benefits
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ASM Benefits
ASM will improve performance
very few sites follow the current best practices ASM will improve system availability
no downtime needed for storage changes
ASM will save you time
it automates a complex DBA task entirely
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Q U E S T I O N SQ U E S T I O N S
A N S W E R SA N S W E R S
Next Steps
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Next Steps.
Automatic Storage Management Demo in the
Oracle DEMOgrounds Pod 5DD
Pod 5QQ
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Reminder please complete the OracleWorldonline session survey
Thank you.
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