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

[Mark Mielke <mark(at)mark(dot)mielke(dot)cc>]

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(at)mielke(dot)cc>