Re: questions about disk configurations

Scott,

> Actually, first I'd try one big RAID 5 and see how it runs. THEN I'd
> spend time mucking around with different configs if that wasn't fast
> enough. If you need x performance and get 10x with a RAID 5 then move on
> to more interesting problems.

Depends on how much time you have to spend re-installing. IMHO, RAID 5 is
slower that straight disks for Postgres, especially with large numbers of
writes. This may not be true for $1000 RAID controllers, but I have yet to
use one.

I have a box with a low-end RAID 5 controller, and it drives like a single IDE
drive on large UPDATE queries. Slower, somethimes.

> Not in my experience. I'd estimate my test box with dual 18 Gig UW scsis
> runs about 1.5 to 1.8 times faster with the two drives in a RAID1 as if
> a single one is used. Bonnie confirms this. single drive can read about
> 25 Megs a second, a pair in a RAID1 reads at about 48 Megs a second.

This is Linux software RAID?

> But as you pointed out in your reply, it's more important to look at how
> he's gonna drive the database. If it has to input hundreds of short
> queries a second, that's a whole different problem than a data warehouse
> with 500 people throwing 8 way joins at the data all day.

Definitely.

--
-Josh Berkus

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