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Intelligent storage system
Intelligent storage systems are the feature rich
RAID arrays that provide highly optimized I/O
processing capabilities.
These storage systems are configured with large
amounts of memory called cache and use
sophisticated algorithms to meet the I/O
requirements of performence sensitiveapplications.
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Components of Intelligent storage system
Front end.
Back end.
Cache. Physical Disks
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Front -end
Intelligent storage system
Port
connectivity
Host
controller
cache
Back end Physical disks
Figure : components of intelligent storage system
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Front end Interface between storage system and the host.
Consists of two components
1) Front end ports.
2) Front end controllers.
Front end ports: enables host to connect to the intelligent storage system.
Each front end port has processing logic that executes the appropriatetransport protocol, such as scsi, fibre channel, or iSCSI for storage
connections.
Redundant ports are provided in front end for high availability.
Front end ports controllers route data to and from cache via the internal databus.
When cache recieves data, the controller sends an ackowledgement message
back to the host.
Controllers optimize I/O processing by using command queuing algorithms.
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Front end command queuing
Command queuing is a technique implemented on front end controllers.
It determines the execution order of recieved commands and can reduce
unnecessary drive head movements and improve disk performance.
When a command is received for execution, the command queuing algorithms
assigns a tag that defines a sequence in which commands should be executed.
Most commonly used command queuing algorithms.
1) FIFO
2) Seek Time optimization
3) Access Time optimization.
In access time optimization commands are executed on the combination of seek
time optimization and analysis of rotational latency for optimal performance.
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Cache Cache is a semiconductor memory where data is
placed temporarily to reduce the time required to
service I/O request from the host.
Cache improves storage system performence by
isolating hosts from the mechanical delaysassociated with physical disks, which are the
slowest components of ISS.
Acessing data from a cache takes less thenmillisecond.
Write data is placed in cache and then written to
disk.
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T a g
R A M
D A T A
S T O R E
P A G E
CACHEDISK
FIGURE: STRUCTURE OF CACHE
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STRUCTURE OF CACHE CACHE consits of
1) Data store.
2) Tag RAM.
Data store holds the data.
Tag RAM indicates where data is found in cache and where the data belongs on the
disk. Tag RAM includes 1) Dirty bit flag 2) Time of last access.
Dirty Bit flag : indicates whether the data in the cache has been commited to the
disk or not
Time of last access: Used to free up information if not accessed for longer period. Cache is organized into pages or slots which is the smallest unit of cache
allocation.
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Read Operation with Cache.