On Wed, Oct 16, 2013 at 6:12 PM, Sage Weil <s...@inktank.com> wrote:
>> 3. During deep scrub of an object with 2 replicas, suppose the checksum is 
>> different for the two objects -- which object wins? (I.e. if you store the 
>> checksum locally, this is trivial since the consistency of objects can be 
>> evaluated locally. Without the local checksum, you can have conflicts.)
>
> In this case we normally choose the primary.  The repair has to be
> explicitly triggered by the admin, however, and there are some options to
> control that choice.

Which options would those be? I only know about ceph pg repair <pg.id>

BTW, I read in a previous mail that...

> Repair does the equivalent of a deep-scrub to find problems.  This mostly is 
> reading object data/omap/xattr to create checksums and compares them across 
> all copies.  When a discrepancy is identified an arbitrary copy which did not 
> have I/O errors is selected and used to re-write the other replicas.

This seems like a right thing to do when inconsistencies are the
result of i/o errors. But when caused by random bit flips, this sounds
like an effective way to propagate corrupted data while making ceph
health = HEALTH_OK.

Is that opportunistic checksum feature planned for emporer?

Cheers, Dan
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