diskeeper

Don't confuse access methodology (cacheing) with file system structure. In short - the Symmetrix has NO impact on filesystem layout. It is really just providing a LUN to your host and servicing reads/writes using cache to increase the response time where possible.

From a Symmetrix perspective it is unlikely defragmentation will help much or at all with writes because unless you have a VERY heavy workload all of your writes are serviced by cache and reordered to the physical disks on the back-end.

However - for random reads which turn into cache misses you could see some performance gain if your OS blocks are defragmented resulting in multiple I/Os (or multiple random misses) going to the Symmetrix. Or even worse what should be a sequential read (i.e. reading the contents of a single large file) could turn into multiple "random" reads due to defragmentation at the filesystem level which could result in slower response times.

Running a defragmenation tool makes as much sense on a Symmetrix as it does on any other disks. Due to cached writes and larger buffer for reads compared to a regular drive you may not see as much impact as you would defragmenting your hard drive on your PC - but on a heavily fragmented system you will see some improvement.

Hope this helps.