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February 1st, 2012 09:00
FAST Cache Statistics
Hello-
We added 2 100 GB SSD drives as FAST Cache a few months ago. Recently, I have been trying to figure out how well they are working. I found a great blog at http://storagesavvy.com/2011/04/12/performance-analysis-for-clariion-and-vnx-%E2%80%93-part-4/ which I followed to gather some statistics on my FAST cache Write and Read hits. Based on my results I was wondering if anyone had any thoughts on how my results rank against theirs/industry standards? My total Write IOPS is anwhere from 800 to 2000 IOPS. Of this amount the FAST Cache Write hits is always around 65 - 70% which seems very good.
My Total Read IOPS is anwhere from 1200 - 5000 IOPS. Of this amount my FAST Read Cache hits is around 15%. Much lower. Looks like I am pretty good on the Write hits with FAST, but not doing so well on read hits with FAST. If this is true any ideas on how I can make improvements?
As an aside I have also sent my .nar files to my SE, but I am curious what the community thinks.
Thank you,
Erik
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kelleg
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February 2nd, 2012 10:00
Your performace numbers for Read look good, but with all things performance related, it depends - on the IO size, the locality of the data (random vs. sequential),. EFD in general performace much better with small block IO"s - 4KB to 16KB. This is the design of SSD in general. It could also mean that more of the Writes are in cache with less room for Read, plus, it takes time for FAST cache to "warm" up - the longer you run, the more likely the right data gets moved to FAST. Backups are no good for FAST.
glen
kelleg
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February 1st, 2012 14:00
What array type (CX4-xxx) and flare version are you running. If CX4 are you at the latest patch level (R30 patch 523)?
Are you using iSCSI or FC for the host connections? If iSCSI have you disabled TCP Delayed ACK on the hosts - this affects host Read performance. Did you put the two EFD disks on two different buses?
glen
elarso
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February 1st, 2012 15:00
We are using a CX4-240 at revision 04.30.000.5.517. Hosts are all connected via FC. Unfortunately, we did not put the EFD's on different buses. They are on BUS 0 which I now realize could also cause issues with my vault drives. I hired EMC pro services to do the install to make sure I didn't do something stupid, but unfortunately they did not call this out.
Do my performance numbers seem low?
Thanks in advance.