We shall soon be moving our storage from Sun A5200 Fibre disk arrays to a HDS 9960. We run Oracle Applications (11i). It is easy to compare the performance now by comparing the run times of certain SQL operations on the same database situated on the SAN and then on the A5200. My question is, how do we ensure that the SAN maintains this level of performance for us and how do we setup an SLA which can be measured. This is important as many, many more servers, etc, will be migrating to the SAN.

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There is a solution called "Dynamic Optimizer" that you can purchase from HDS. Dynamic Optimizer is a tool that runs in the firmware of the storage array and monitors all I/O going through the subsystem. The optimizer continually monitors for "hot spots" in the array and then migrates the data automatically to remove the hot spot. It can dynamically move data while the application is online from say a RAID5 disk to a RAID 0+1 disk to keep performance at peak.

There are two modes of operation you can enable. Automatic mode dynamically tunes the box for you so that DBAs can finally forget about the details of I/O performance tuning. The other mode is interactive mode, where the subsystem will notify you that a hot spot condition exists and will ask you what you would like to do. You can either manually move the data yourself or let the dynamic algorithm determine the best placement for you.

The good news is that due to the internal switched architecture of the storage array, many servers can be added without impacting performance of other servers. This is due to the "point-to-point" nature of a switch. You can think about the array being like a network switch vs. a network hub. You can add more "stuff" to a switch. A hub uses shared resources and contention for those resources can occur when more than one initiator is connected.

Chris

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This was first published in March 2002

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