In my opinion, i would go with the FASTCache.  when you used SSd for FASTCache, it will benefit all the lun's on the array and not just one or two that you carve into a raid group or FAST pool.

If you went with normal FAST, then you would be limited to the amount of space that is allocated to the pool.

there are mininum number of disk requirements for FASTCache since it places those disks in a raid 10 config.  for FAST, you can use R5, R6,or R10 so you have some play room.

hope this helps

I would recommend reviewing the "EMC CLARiiON and Celerra Unified FAST Cache - A Detailed Review" available on PowerLink.

http://powerlink.emc.com/km/live1/en_US/Offering_Technical/White_Paper/h8046-clariion-celerra-unified-fast-cache-wp.pdf

glen

PS - on PowerLink - do a search for "FAST Cache" - there are a lot of new documents now available - use cases

Message was edited by: kelleg

Tiny correction to a comment made above.  FAST Cache creates RAID 1 mirrors (and not RAID 10).  So every 2 disks is an independent RAID Group, and not 1+1 (yes, the engineers could have chosen this also), 2+2, ... 8+8 configurations possible with a RAID 10 RG.  Then private luns are bound on these separate RAID Groups to hold the warm blocks.

i found i have already read this white paper, .

below is the key point:

FAST Cache focuses on improving performance while FAST focuses on improving TCO.

and, in my opinion, if you have not much money or if you definitely know where's your hot spot data（index etc）, you can put it directly on SSD disk whiout buying FAST or FAST cache.

All good performance admins should be aware of any hot spots in the array. SSD performance will slow as the disk starts to fill up due to wear leveling. Random Read i/o remains fast when the drive is full- Random write becames impacted.