On Thu, 25 Aug 2005, Walt Reed wrote:
> On Thu, Aug 25, 2005 at 02:22:16PM +0100, Tony Finch said:
> > On Thu, 25 Aug 2005, Walt Reed wrote:
> >
> > > In addition to other suggestions that were put forth, making sure your
> > > RAID controller has battery backed write cache does AMAZING things for
> > > performance.
> >
> > And check the disk write caches are turned off :-)
>
> How so? I found the write cache sped most things up a LOT... Found it
> helped my database by a factor of 2. Added the cache on all my machines
> and overall load levels have dropped (as reported by MRTG. Especially
> the IOWait state.)
If you have a battery-backed write cache on the controller, you don't need
or want a volatile write cache on the disks. The additional cache on the
disks will not improve performance and will reduce reliability. If the
disks lie to the controller about when data has hit stable storage then
the battery will not protect you from losing data in the event of a power
outage.
http://www.livejournal.com/community/lj_dev/670215.html
http://www.livejournal.com/users/brad/2116715.html
Tony.
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