UFS2 metadata checksums

[Pawel Jakub Dawidek]

On Fri, Apr 24, 2009 at 02:51:58AM -0400, Scott Burns wrote:
> 
> Andrew Snow wrote:
> >
> >Ideally you would implement complete disk checksumming as a GEOM device.
> >
> >Then you could layer geom_mirror on top of it, so that if the checksum 
> >fails and returns EIO, geom_mirror can try the alternate device and 
> >rebuild the one with the bad checksums.
> >
> >That will then complete the feature set implemented by ZFS, but for any 
> >filesystem on top of GEOM.
> >
> >- Andrew
> >
> 
> The geli(8) GEOM class is able to verify sectors (and I believe it 
> returns EINVAL on ones that fail), but with a noticeable performance 
> impact.  I could certainly see the use for a GEOM class that just does 
> simple checksumming.  If gmirror can then be aware of it, that does 
> provide functionality similar to a ZFS mirror.

Geli uses strong cryptography for integrity verification, which is not
needed in this case. The class that does that still needs to use
the method I implemented in geli to provide atomicity.

Gmirror is already "aware" of that - in case of an error on one half, it
will use the other half. What gmirror doesn't do (and ZFS does) is
self-healing.

All in all, in my opinion GEOM class is much better for this - it will
protect everything (metadata and data) and will be file system
idenpendent.

-- 
Pawel Jakub Dawidek                       http://www.wheel.pl
pjd at FreeBSD.org                           http://www.FreeBSD.org
FreeBSD committer                         Am I Evil? Yes, I Am!
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