Re: With 4 disks should I go for RAID 5 or RAID 10 - Mailing list pgsql-performance

From Mark Mielke
Subject Re: With 4 disks should I go for RAID 5 or RAID 10
Date
Msg-id 47728000.4000709@mark.mielke.cc
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In response to With 4 disks should I go for RAID 5 or RAID 10  ("Fernando Hevia" <fhevia@ip-tel.com.ar>)
Responses Re: With 4 disks should I go for RAID 5 or RAID 10
Re: With 4 disks should I go for RAID 5 or RAID 10
List pgsql-performance
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@mielke.cc>

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