Re: more 10K disks or less 15K disks

All the disks are usually laid out in a single RAID 10 stripe . There
are no dedicated disks for the OS/WAL as storage is a premium

On Wed, Apr 28, 2010 at 10:30 PM, Greg Smith <greg(at)2ndquadrant(dot)com> wrote:
> Anj Adu wrote:
>>
>> We do not archive the WALs. We use application-level replication to
>> achieve redundancy. WAL archiving was difficult to support with the
>> earlier hardware we had ( 6x300G 10K disks Dell 2850) given the
>> volumes we were dealing with. The RAID card should be from the same
>> manufacturer (LSI in Dell's case).
>>
>
> The database is generating WAL files that are written to the pg_xlog
> directory.  Sometimes this is broken out into a separate drive so that it's
> possible to measure how much I/O is being written to there, as opposed to
> the main database drive.  That's the WAL writing I was asking about, not the
> overhead of archiving WAL files to elsewhere.  The way that WAL writes go to
> disk, you can't always speed them up just by throwing more disks at
> them--sometimes, you just need the individual disk involved to be as fast as
> possible.
>
> You should try to get the same Dell RAID controller you're already using,
> that you know delivers good performance running your app.  All I've heard
> about the models released after the Perc 6i has been bad news.  Dell varies
> how much they tinker with the LSI firmware in their own version of each
> card, and they didn't do very much of that in the Perc 6 series.  They seem
> to be changing around the newer models more again, which is always bad news.
>
> --
> Greg Smith  2ndQuadrant US  Baltimore, MD
> PostgreSQL Training, Services and Support
> greg(at)2ndQuadrant(dot)com   www.2ndQuadrant.us
>
>