Monday 28 September 2009

Oracle 11gR2 - Flash Cache

Ok so those who followed Oracle's Exadata v2 pitch will have seen something mentioned in the specs re FlashCache and it's use of SSD storage. There's little major stuff around but some brief info can be found at :-
Now the part that is of particular interest to me is, if or when, this feature is made available as part of the normal Oracle 11gR2 release train.

This slide from appears to show that the FlashCache is interfaced through a file location, thus one assumes it could be stored on any device that is file-interface accessible (eg an array based SSD or a host based SSD).

Now this is where it gets interesting for me, in that in a similar way to OpenZFS L2Arc , a local server SSD could be used as a high speed L2 SGA extension without putting any data at risk.

Server SSDs are supposedly not in the same league as array EFDs, but ignoring that (be it real or not), the price point of SSD in servers (compared to that of those in arrays) combined with this very easy use case model (both setup and ongoing mngt very simple) and lack of risk of data loss (re these use cases), certainly makes it a very intriguing proposition and something on my 'benchmark' and TCO evaluation list very shortly.

My test case would be to take an x86 server running OpenSolaris and place 2x256GB SSDs into it and then run Oracle Swingbench & Orion with :- no SSD usage, 1 for L2Arc, 2 for L2Arc, 1 for FlashCache, 2 for FlashCache, 1 for L2Arc & 1 for FlashCache. Also interested to test 2xFlashCache with ASM Vs 2xL2Arc without ASM. Intrigued to see what the performance impacts will be :)

Naturally I'm also keen to understand & compare these costs & benefits against those of Oracle InMemoryDatabase (eg TimesTen) and array based SSD.

My personal suspicion is that using the SSDs for L2Arc & FlashCache (if / when available) will deliver good benefits cases, and then once the storage array firmware has achieved it's required SSD mngt & usability maturity we'll be able to use array based SSDs in addition to server based for even further combined benefits.

I'd be interested to hear about other people's experiences, thoughts & plans in this area...

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1 comment:

  1. As far as I know the SSD's sold as "EFD"s (enterprise flash devices) are the Stec Zeus IOPS disks. There are other SSD's out there, but from what I've seen the Zeus disks are the pick of the bunch today. Having said that I dont think they're worth the premium price the EFD tag brings.