Re: SSD + RAID

On 11/13/09 10:21 AM, "Karl Denninger" <karl(at)denninger(dot)net> wrote:

>
> One caution for those thinking of doing this - the incremental
> improvement of this setup on PostGresql in WRITE SIGNIFICANT environment
> isn't NEARLY as impressive. Indeed the performance in THAT case for
> many workloads may only be 20 or 30% faster than even "reasonably
> pedestrian" rotating media in a high-performance (lots of spindles and
> thus stripes) configuration and it's more expensive (by a lot.) If you
> step up to the fast SAS drives on the rotating side there's little
> argument for the SSD at all (again, assuming you don't intend to "cheat"
> and risk data loss.)

For your database DATA disks, leaving the write cache on is 100% acceptable,
even with power loss, and without a RAID controller. And even in high write
environments.

That is what the XLOG is for, isn't it? That is where this behavior is
critical. But that has completely different performance requirements and
need not bee on the same volume, array, or drive.

>
> Know your application and benchmark it.
>
> -- Karl
>