Re: SSD + RAID

The FusionIO products are a little different. They are card based vs trying to emulate a traditional disk. In terms of volatility, they have an on-board capacitor that allows power to be supplied until all writes drain. They do not have a cache in front of them like a disk-type SSD might. I don't sell these things, I am just a fan. I verified all this with the Fusion IO techs before I replied. Perhaps older versions didn't have this functionality? I am not sure. I have already done some cold power off tests w/o problems, but I could up the workload a bit and retest. I will do a couple of 'pull the cable' tests on monday or tuesday and report back how it goes.

Re the performance #'s... Here is my post:

http://www.kennygorman.com/wordpress/?p=398

-kg

>In order for a drive to work reliably for database use such as for
>PostgreSQL, it cannot have a volatile write cache. You either need a
>write cache with a battery backup (and a UPS doesn't count), or to turn
>the cache off. The SSD performance figures you've been looking at are
>with the drive's write cache turned on, which means they're completely
>fictitious and exaggerated upwards for your purposes. In the real
>world, that will result in database corruption after a crash one day.
>No one on the drive benchmarking side of the industry seems to have
>picked up on this, so you can't use any of those figures. I'm not even
>sure right now whether drives like Intel's will even meet their lifetime
>expectations if they aren't allowed to use their internal volatile write
>cache.
>
>Here's two links you should read and then reconsider your whole design:
>
>http://www.mysqlperformanceblog.com/2009/03/02/ssd-xfs-lvm-fsync-write-cache-barrier-and-lost-transactions/
>http://petereisentraut.blogspot.com/2009/07/solid-state-drive-benchmarks-and-write.html
>
>I can't even imagine how bad the situation would be if you decide to
>wander down the "use a bunch of really cheap SSD drives" path; these
>things are barely usable for databases with Intel's hardware. The needs
>of people who want to throw SSD in a laptop and those of the enterprise
>database market are really different, and if you believe doom
>forecasting like the comments at
>http://blogs.sun.com/BestPerf/entry/oracle_peoplesoft_payroll_sun_sparc
>that gap is widening, not shrinking.