Re: BBU Cache vs. spindles

On Oct 7, 2010, at 4:38 PM, Steve Crawford wrote:

> I'm weighing options for a new server. In addition to PostgreSQL, this machine will handle some modest Samba and Rsync load.
>
> I will have enough RAM so the virtually all disk-read activity will be cached. The average PostgreSQL read activity will be modest - a mix of single-record and fairly large (reporting) result-sets. Writes will be modest as well but will come in brief (1-5 second) bursts of individual inserts. The rate of insert requests will hit 100-200/second for those brief bursts.
>
> So...
>
> Am I likely to be better off putting $$$ toward battery-backup on the RAID or toward adding a second RAID-set and splitting off the WAL traffic? Or something else?

A BBU is, what, $100 or so? Adding one seems a no-brainer to me. Dedicated WAL spindles are nice and all, but they're still spinning media. Raid card cache is waaaay faster, and while it's best at bursty writes, it sounds like bursty writes are precisely what you have.