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From Florian Weimer <fwei...@bfk.de>
Subject Re: Support for filesystem snapshots (?)
Date Tue, 03 Aug 2010 10:33:28 GMT
* Les Mikesell:

>> When I speak of a filesystem snapshot, I mean an instantaneous copy
>> of the volume (ala NetApp, EMC, ZFS).  In this case, there is a
>> guarantee that if we snap the new "current", then we will also have
>> the other files (assuming that they have been flushed, etc, by the
>> client).  Further, it sounds like (a) subsequent commits will not
>> run into trouble because of the partial commit, and (b) the
>> repository will not be otherwise affected by a partial commit.
>>
>> That means filesystem snapshots pass the transactional test.
>
> Maybe - is there a guarantee that the app flushes to disk in the
> expected order?  Or do snapshots take the current dirty filesystem
> buffers into account?

Kernel-level buffers are taken into account.  Application buffers
aren't, the application has to take care of that.  But if the
Subversion fails to do that, it cannot recover from file system
crashes, either, which is arguably a bug in Subversion.

-- 
Florian Weimer                <fweimer@bfk.de>
BFK edv-consulting GmbH       http://www.bfk.de/
Kriegsstra├če 100              tel: +49-721-96201-1
D-76133 Karlsruhe             fax: +49-721-96201-99

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