[Dirvish] Heads up for DST if you backup to/from FAT/NTFS filesystems

Keith Lofstrom keithl at kl-ic.com
Mon Mar 28 09:09:29 PST 2005

On Mon, Mar 28, 2005 at 06:09:34PM +0200, Eric Mountain wrote:
... [ daylight savings time ] ...
> I got hit because I have a dual boot machine which has the hardware clock on 
> UTC.  I run dirvish under Linux and backup part of the Windows ME FAT 
> filesystem (My Docs).  rsync considered that all files had changed and 
> created a new copy of all files on the backup.
> The fix was of course to add:
> rsync-option:
>  --modify-window=3600
> to the conf file for the MyDocs backup.  

Good (if scary!) observation.

To clarify, I assume you are talking about backing up the windows
partition on a dual-boot backup *client* to a dirvish/rsync backup
server on a  different machine.  This sounds like something that
really ought to be fixed at the application level rather than the 
configuration level, perhaps in cygwin+rsync.  We should be comparing
the time data structures on the disk, not the interpretation of them
by the client or server OS.  We should not rely on anything that
could be affected by the settings of any hardware or software clock.

But it gets worse.  If I move a backup client from Oregon to Japan
(across the date line), I should not get a new copy of the files on
the dirvish server.  Since I can imagine a situation where the reported
time can change by 23 hours, and I may want to back up every 4 hours,
the --modify-window strategy will not always work.  It is certainly a
lot better than nothing, though.  Thanks for making us aware of both
the problem and a pretty good solution.  Remind me to put something
in the FAQ about it.


Keith Lofstrom          keithl at keithl.com         Voice (503)-520-1993
KLIC --- Keith Lofstrom Integrated Circuits --- "Your Ideas in Silicon"
Design Contracting in Bipolar and CMOS - Analog, Digital, and Scan ICs

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