in the CLARiiON Best Practices for FC Storage the topic "Disk Alignment" is well described.
We are considering the use of virtual provisioning on our new CLARiiON systems. Are disk crossings and disk alignment still issues than?
The short answer is, No. Alignment is a performance optimization. A user choosing and provisioning VP does not have the fine-level of control over the LUN with VP needed to align it.
If your workload has the I/O profile that would benefit from alignment, and requires a higher-level, and more deterministic performance than available with VP, a traditional RAID group/LUN should be provisioned.
Thin LUNs cannot be aligned because of the way storage is incrementally allocated from the pool of available storage. Any alignment performed by a file system will have not effect.
The whitepaper EMC CLARiiON Virtual Provisioning in its Thin LUNs section describes how storage is allocated. This paper is available on PowerLink.
jps00
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Posted October 12th, 2009 06:00
If your workload has the I/O profile that would benefit from alignment, and requires a higher-level, and more deterministic performance than available with VP, a traditional RAID group/LUN should be provisioned.