[Linux-cluster] redundancy in redhat clusters

[Jonathan E Brassow]

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