Re: SATA drives performance

2009/12/24 Ognjen Blagojevic <ognjen(at)etf(dot)bg(dot)ac(dot)yu>:
> Hi all,
>
> I'm trying to figure out which HW configuration with 3 SATA drives is the
> best in terms of reliability and performance for Postgres database.
>
> I'm thinking to connect two drives in RAID 0, and to keep the database (and
> WAL) on these disks - to improve the write performance of the SATA drives.
>
> The third drive will be used to reduce the cost of the RAID 0 failure
> without reducing the performance. Say, I could configure Postgres to use the
> third drive as backup for WAL files, with archive_timeout set to 15 minutes.
> Daily backups will be created on different server. Loss of last 15 minute
> updates is something the customer can afford. Also, one day restore time is
> case of failure is also affordable (to reinstall the OS, Postgres, restore
> backup, and load WALs).
>
> The server will be remotely administered, that is why I'm not going for RAID
> 1, 1+0 or some other solution for which, I beleive, the local administion is
> crucial.
>
> Server must be low budget, that is why I'm avoiding SAS drives. We will use
> CentOS Linux and Postgres 8.4. The database will have 90% of read actions,
> and 10% of writes.
>
> I would like to hear your opinion, is this reasonable or I should reconsider
> RAID 1?

If you're running RAID-0 and suffer a drive failure, the system
becomes somewhat less cheaper because you now have to rescue it and
get it up and running again. I.e. you've moved your cost from
hardware to your time.

I'd recommend RAID-1 with a 3 disk mirror. Linux now knows to read
from > 1 drive at a time even for a single user to get very good read
bandwidth ( I routinely see read speeds on a pair of WD Black 7200 RPM
SATA drives approaching 200MB/s (they are ~100MB/s each). Your
redundancy is increased, so that should one drive fail you're still
completely redundant. Also 1TB drives are CHEAP nowadays, even the WD
blacks and similar drives from other manufacturers. If you need more
storage than a single 1TB drive can provide, then you'll need some
other answer.