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Re: [Linux-cluster] redundancy in redhat clusters

got it. good point.
why do you think raid5 would give poor performance ?
as long as it is not in degredation mode the performance scales
to n-1 disks.


On 11/30/05, Jonathan E Brassow <jbrassow redhat com> wrote:

On Nov 29, 2005, at 9:19 AM, Raz Ben-Jehuda(caro) wrote:

> Question:
> I need to add to a clsutered environment redundancy.
> Since the native linux raid 5 is not clustered awared,
> what would make it aware to the cluster ?
> What does it lack ?

Clustered file systems and applications will ensure that they are not
doing simultaneous writes to the same [meta-]data.  However, they have
no way to tell that a write to one area will conflict with the write to
another because of the stripe width and parity calculation of the RAID
device.  This will lead to parity block corruption.

To solve this problem, the RAID 5 implementation must be cluster aware
and take out single-writer/multiple-reader locks on the stripes -
ensuring that multiple machines are not writing to the same stripe at
the same time.

The performance of a cluster-aware software RAID 5 is likely to be
abysmal, and will probably not rank very high on anyone's priority

A mirroring solution is in the works, and later, dd-raid may become a


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