Re: How to improve db performance with $7K? - Mailing list pgsql-performance

From Jacques Caron
Subject Re: How to improve db performance with $7K?
Date
Msg-id 6.2.0.14.0.20050418192528.04238088@pop.interactivemediafactory.net
Whole thread Raw
In response to Re: How to improve db performance with $7K?  (Alex Turner <armtuk@gmail.com>)
Responses Re: How to improve db performance with $7K?
Re: How to improve db performance with $7K?
List pgsql-performance
Hi,

At 18:56 18/04/2005, Alex Turner wrote:
>All drives are required to fill every request in all RAID levels

No, this is definitely wrong. In many cases, most drives don't actually
have the data requested, how could they handle the request?

When reading one random sector, only *one* drive out of N is ever used to
service any given request, be it RAID 0, 1, 0+1, 1+0 or 5.

When writing:
- in RAID 0, 1 drive
- in RAID 1, RAID 0+1 or 1+0, 2 drives
- in RAID 5, you need to read on all drives and write on 2.

Otherwise, what would be the point of RAID 0, 0+1 or 1+0?

Jacques.



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