At the recent EMC conference at a session about Clariions, they indicated several things about Clariions that I thought I would share. From my notes . . . .
1) Raid 0+1 is better for writes, but doesn't help with reads. It will only/mostly use just one copy for reads. It's not as smart as a dmx/symm, which will perform reads from both copies. Raid 5 random reads are just as good as 0+1 random reads. 2) Raid 3. The way I heard it explained, r3 was recommended for big block sequential processing (like tsm staging pools) for ATA drives. The reasoning was that ATA drives don't currently have command tag queueing. Since they can only do one i/o op at a time, r3 fits real well with this. They recommended this for up to around 10 concurrent data streams to the raidset. The quote went something like this: ATA drives are brain dead, and raid 3 optimizes their brain-deadness. 3) Raid 5 on Fiber Channel drives is very good with large block sequential I/O. Raid 3 is not needed here. 4) Raid5 definitely has the write performance penality, which requires 4 i/o's per random write (not writing a full strip). This is hidden behind the write cache and performed later. They gave a rule of thumb of using raid5 for random I/O up to a write/read ratios of around 25-30%. That is, a random access pattern where there is 70% reads and 25% writes. 5) Leave the raidset strip size at the default (I think it's 64k, or 128 blocks). They have performed all kinds of internal testing and this is the optimum size for Clariion raid 5 raidsets. Period. The internal processing logic of the Clariion is optimized for this strip size - don't mess with it unless you reallllllly know what you are doing. 6) 15k rpm fc drives give around a 30% increase in small block random iops than 10k drives. Rick ----------------------------------------- The information contained in this message is intended only for the personal and confidential use of the recipient(s) named above. If the reader of this message is not the intended recipient or an agent responsible for delivering it to the intended recipient, you are hereby notified that you have received this document in error and that any review, dissemination, distribution, or copying of this message is strictly prohibited. If you have received this communication in error, please notify us immediately, and delete the original message.
