Re: mismatch_cnt again

Goswin von Brederlow
2009-11-16T05:21:03Z

Neil Brown <neilb@suse.de> writes:

> On Sun, 15 Nov 2009 17:29:17 -0500
> "Guy Watkins" <linux-raid@watkins-home.com> wrote:
>
>> I have been following this issue some, and I think this could be a
>> cause for silent corruption on RAID5 and RAID6. I don't think this
>> has been mentioned, if so, sorry.
>
> RAID1/RAID10 are very different from RAID5/RAID6
>
> RAID1/RAID10 can get 'mismatches' due to the particular behaviour
> of swap or filesystems. However this doesn't matter (the blocks that
> are inconsistent are of no interest to the filesystem).
>
> RAID5/RAID6 is careful not to allow any mismatches to creep in
> due to any particular filesystem or swap activity. This is because,
> as you say, those mismatches could be significant to the RAID
> algorithm even though they might be of no interest to the filesystem.
>
> mismatches can only occur in a RAID5/RAID6 due to a software bug
> in the md/raid code, or due to 'hardware errors' (including of course
> drive firmware errors etc).
>
> NeilBrown

Does that mean raid4/5/6 always coppies the data or that it protects
it with the MMU?

MfG
Goswin