[dm-devel] Desynchronizing dm-raid1
Martin K. Petersen
mkp at mkp.net
Mon Apr 7 17:44:27 UTC 2008
>>>>> "Malahal" == malahal <malahal at us.ibm.com> writes:
Malahal> Your problem is very similar to an iSCSI problem sumitted
Malahal> here:
Malahal> http://now.netapp.com/NOW/cgi-bin/bol?Type=Detail&Display=137902
Can't see it without a netapp account...
Malahal> Fortunately, you can detect the problem and the I/O can be
Malahal> retried if possible.
That's not entirely trivial. Obviously the original data that matches
the checksum is gone. And I don't want to blindly regenerate the
checksum from the new data (how do I know this was an "ok" kind of
corruption?).
The only one that has that knowledge is the filesystem. And if the
filesystem needs to be integrity-aware, I'd much rather have it Do The
Right Thing than teach it to inspect and reissue I/Os that come back
with -EDANGERWILLROBINSON.
With ext2 at least this is not some rare corner case. It happens
hundreds of times during an unpack of a kernel tarball. We'd end up
burning many, many cycles doing retries.
--
Martin K. Petersen Oracle Linux Engineering
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