Re: SSD + RAID

Dan Langille wrote:
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> Bruce Momjian wrote:
> > Matthew Wakeling wrote:
> >> On Fri, 13 Nov 2009, Greg Smith wrote:
> >>> 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.
> >> Seagate are claiming to be on the ball with this one.
> >>
> >> http://www.theregister.co.uk/2009/12/08/seagate_pulsar_ssd/
> >
> > I have updated our documentation to mention that even SSD drives often
> > have volatile write-back caches. Patch attached and applied.
>
> Hmmm. That got me thinking: consider ZFS and HDD with volatile cache.
> Do the characteristics of ZFS avoid this issue entirely?

No, I don't think so. ZFS only avoids partial page writes. ZFS still
assumes something sent to the drive is permanent or it would have no way
to operate.

--
Bruce Momjian <bruce(at)momjian(dot)us> http://momjian.us
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+ If your life is a hard drive, Christ can be your backup. +