Re: RAID 5 and postgresql

On Wed, 2006-01-18 at 10:46, Hrishikesh Deshmukh wrote:
> Hi All,
>
> Are there any pointers for RAID tuning (RAID5) with PostgreSQL 8.0?!

There's a bi monthly conversation on this subject here and in the
perform list. I'd recommend searching the perform list on the subject.
Here's the short version:

1: Get the best RAID card you can afford. Battery backed cache is
important for good write performance.

2: In many circumstances, RAID 10 is a much better choice than RAID5.
However, some RAID cards are notoriously bad at layering RAID levels.
So is the linux kernel, unless some one fixed that. The solution to
this problem is often to run one layer in hardware, and the other in the
OS. I.e. take 10 drives. Build 5 mirror sets on the hardware
controller. Build a RAID 0 strip set out of them in the linux kernel
layer.

3: RAID5 is a decent choice for a reporting / mostly read database.

4: Lately, the Areca cards seem to be getting a lot of good marks. The
LSI and Escalade cards are pretty good. I've had horrible luck with
Adaptec, but some folks have had better luck than me.

5: For RAID 5 to perform well with lots of writes, you need plenty of
drives and that battery backed cache mentioned above. With fewer than 8
or 10 drives, the RAID 10 will always be much faster.

6: Drives are cheap, data ain't, so you may be better off with RAID
10. At least have a look at it.