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Re: Taking mirror Backup of SVN Repos through 3rd Party Software

From: Les Mikesell <lesmikesell_at_gmail.com>
Date: Thu, 30 Jun 2011 11:26:36 -0500

On 6/30/2011 10:39 AM, Daniel Shahaf wrote:
>>> Read the attached issue. FSFS on 1.7 is affected --- specifically,
>>> revprops.db, which contains the only copy of revprops of packed
>>> revisions.
>> A backup made in an inconsistent state should exactly resemble the
>> disk files if the system lost power or crashed for another reason at
>> that point. What are you supposed to do in that very likely
>> circumstance?
> SQLite guarantees ACID in the event of a power failure. Given that,
> what do you think FSFS should do to handle a power failure during
> a revprop edit?

What has to happen to make the system consistent? Whether the change
completes or not only matters if the client records the success and
behaves differently later.

> When you say "backup", do you mean "An atomic snapshot of the disk's
> state", 'cp -a', or something else?

I guess I'm really talking about the state of the disk after the restore
of a filesystem backup. To me, that would usually be an rsync-based
copy which isn't atomic at all but if it is repeated until it doesn't
report any changes I expect it to represent a consistent state - and
generally I expect it to work anyway. On most filesystems on most
hardware, I don't have any particular expectations about the filesystem
state after a crash. Things that appeared consistent when accessed
through the running filesystem cache may not have been committed to disk
or that may have happened in a different order than expected.

    Les Mikesell
Received on 2011-06-30 18:27:19 CEST

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