How to review FAST Cache performance ?

Question

Friends,

I 'm finally managing some real storage stuff again and one of the CX4's I have has FAST Cache on board !

I'm using Solarwinds Profiler and I must say it's a very good tool to get quick access to performance data,

but

I'd like to know if my FAST Cache is actually doing something. I can see the 2 SSD's perform around 2500 IOps, but I'm not seeing a degradation in disk usage of the raid groups which are using FAST Cache. I'd expect the RGs that were very busy before to show a decrease in %utilization, but I don't see it.

Does anyone have experience with FAST Cache and how to measure the effectiveness of the SSDs. Customers would like to know what they're paying for and so do I.

christopher_ime · Accepted Answer

Simply wanted to add to Avi's comment about how to obtain this information from Unisphere Analyzer. There is a great series on using Analyzer and also goes into generating useful Excel graphs from the exported data; however, specific to this thread is a quick walk-through that, in the author's own word's, demonstrates "... how to tease FASTCache performance data out of Analyzer."

http://storagesavvy.com/2011/05/24/performance-analysis-for-clariion-and-vnx-%E2%80%93-part-5-fastcache/

Also, just wanted to make a small (but subtle) correction to a comment made above about FAST Cache. From the selected drives, it actually creates private RAID 1 rg's (and not RAID 10).

Kumar_A · Answer

After you install FAST Cache, Unisphere Analyzer gathers FAST Cache statistics to help you monitor FAST Cache performance. To view these statistics, you must enable Analyzer’s Advanced mode. To enable Analyzer’s Advanced mode: In Unisphere click the Monitoring tab; in the Analyzer section click Customize Charts; click the General tab; and select the Advanced checkbox.

For a list of all FAST Cache statistics, you can check the FAST Cache whitepaper on Powerlink.

RRR · Answer

Thanks. I was hoping for a 'cheaper' way to do a fast check on it's performance, but I guess Analyzer is always the best option. I'm seeing dirty cache pages on Fact Cache of 30 to 35%, I guess this is still low, right ?

kelleg · Answer

It's low, but that seems about normal from what I've seen on other arrays - you need to look at the disks in the raid groups with FAST enabled and look at the disk IOPS. That's what fast should be intercepting.

You should also be careful not to overload any one BUS - putting all the SSD's on one bus for FAST cache could overload it - this can affect performance if you use BUS 0 - the vault drive BUS.

glen

kelleg · Answer

Just to be safe - use different buses for each EFD - fast internally is a R10 so spliting the disks between DAE's and BUSes will provide extra protection glen

dynamox · Answer

Glen,

i have a VNX5700 on its way that will have a couple of DAE and some EFDs for Fast cache, so do you recommend that i move drives that will be used for fast cache to a different DAE ..other than bus 0 ? Let's say i have 2 x 200G EFD ..should i put them on different buses ?

Kumar_A · Answer

A VNX5700 can have four backend busses, so it will be recommended that you split the flash drives across multiple busses. FAST Cache can potentially generate a lot of backend IO and you dont want to limit FAST Cache performance because of a saturated backend bus.

dynamox · Answer

well, i am not buying a fully populated box so i may not have a choice but to put some EFDs on bus 0.

RRR · Answer

I am looking at the disk level and I'm seeing that my SSDs are indeed performing at 2 or 3k IOps, but at the disk level of the RGs on which the LUNs reside for which I enabled FAST Cache, I'm not seeing any difference.

So all I see is the SSDs drawing IOps, but for the rest I don't notice anything.

RRR · Answer

Nice tip !!

CLARiiON

How to review FAST Cache performance ?

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