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Re: [Linux-cluster] redundancy in redhat clusters




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 list.

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

 brassow


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