GEOM + RAID5 help

[Greg 'groggy' Lehey]

On Saturday, 21 February 2004 at 16:40:56 +0100, Lukas Ertl wrote:
> Hi,
>
> I'm currently implementing the RAID5 bit of geom_vinum, and I could use a
> little help.  One problem I'm faced is that if the subdisk where the
> original request should go to is down, I need to read all the other
> stripes, recalculate the parity with the original data, and then write the
> parity stripe (in the BIO_WRITE case), or read all other stripes plus the
> parity to recalculate the desired data (in the BIO_READ case).

You don't need to have a disk down to have this issue.  When writing a
RAID-5 block, you almost always need to do something similar.  Look at
complete_raid5_write() in vinuminterrupt.c for how it's done now.

Greg
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