Re: FFS corruption

[Mouse <mouse%Rodents-Montreal.ORG@localhost>]

>>> After this migration, the filesystem started corrupting the same
>>> file /usr/pkg/etc/httpd/httpd.conf at the same time, which happens
>>> to be /etc/daily end of execution.
>> Which filesystem?  The original or the copy?
> The copy.  It would blow my mind if making a copy of a VM could break
> the original.

Strictly speaking, yes.  But you not only copied the data off the
source VM - which, yes, should not break anything - you also wrote it
to the destination.  I can imagine cases where that writing is what
caused the trouble.  Writing data to the destination might do this if,
for example, the destination is another VM ultimately backed by the
same spindle and there is something wrong with a driver that causes it
to confuse nominally-distinct disk blocks with one another (like my
possibility 2).

>> [With Xen] that there's at least one more layer of mapping between
>> OS sector numbers and hardware sector numbers
> Indeed; the domU filesystem is a file in the dom0 filesystem.

Hm.  That does make it more difficult to come up with a plausible
failure mode to explain this.  Have you tried creating another file in
the dom0 filesystem of the same size with easily identifiable content,
to see if any of that content appears in the affected domU filesystem?

dholland's identification of the overwrite data as inodes certainly
does feel provocative, but I'm not sure what to make of it.

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