Re: With 4 disks should I go for RAID 5 or RAID 10

Mark Mielke <mark@xxxxxxxxxxxxxx> · Wed, 26 Dec 2007 11:23:28 -0500

Title: With 4 disks should I go for RAID 5 or RAID 10

Fernando Hevia wrote:

  Database will
be about 30 GB
in size initially and growing 10 GB per year. Data
is inserted overnight in
two big tables and during the day mostly read-only queries are run. Parallelism is
rare.

  I have read about different
raid levels with Postgres but the advice found seems
to apply on 8+ disks systems. With only four disks and performance in mind should I build a RAID 10 or RAID 5 array? Raid 0 is overruled since redundancy is needed.
  I am going to use software
Raid with Linux (Ubuntu Server 6.06). 

In my experience, software RAID 5 is horrible. Write performance can
decrease below the speed of one disk on its own, and read performance
will not be significantly more than RAID 1+0 as the number of stripes
has only increased from 2 to 3, and if reading while writing, you will
not get 3X as RAID 5 write requires at least two disks to be involved.
I believe hardware RAID 5 is also horrible, but since the hardware
hides it from the application, a hardware RAID 5 user might not care.

Software RAID 1+0 works fine on Linux with 4 disks. This is the setup I
use for my personal server.

Cheers,

mark

-- 
Mark Mielke <mark@xxxxxxxxx>