unit2-san-intelligent-storage-system

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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.



Components of Intelligent storage system

Front end.

Back end.

Cache. Physical Disks



Front -end

Intelligent storage system

Port

connectivity

Host

controller

cache

Back end Physical disks

Figure : components of intelligent storage system



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.



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.



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.



T a g

R A M

D A T A

S T O R E

P A G E

CACHEDISK

FIGURE: STRUCTURE OF CACHE



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.



Read Operation with Cache.

unit2-san-intelligent-storage-system

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