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Re: changing raid level?

On Tue, Jan 27, 2009 at 01:23:37PM -0600, Greg Oster wrote:
>   [...]
> For a RAID 1 set, the "parity unit" is simply the second disk, and 
> computing that parity requires no further computations.

On a slow CPU the read+read+compare+write is killing the whole system
(mostly the "compare" I think) with 90% of the cpu working on this.
A simple read+write is much, much better on such a setup (the system
is still useable while doing a raid1 reconstruct). It matters
even on a fast CPU, when both disks are able to provide data at 180MB/s.
The system is still useable but comptationnal tasks (esp. network
encryption) is much, much slower.

Manuel Bouyer, LIP6, Universite Paris VI.  
     NetBSD: 26 ans d'experience feront toujours la difference

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