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Bug#661266: Fstransform and backup



Hi.

About the description of fstransform package in [1]: fstransform can do
the conversion of a filesystem in place and without the need of a
backup. Of course there is some possibility that the operation
encounters some error (which could bring the partition in an
inconsistent state, from which recover could be difficult or even nearly
impossible), so a backup is heavily encouraged. But if you decide to
risk and have luck, you can actually do a filesystem conversion without
copying files out of the partition.

 [1] http://bugs.debian.org/cgi-bin/bugreport.cgi?bug=661266

Fstransform works exploiting the sparse files feature of both original
and target filesystems: it creates a sparse file in the original
filesystem, of the same size as the whole partition itself. Then if
formats it using the target filesystem and start copying files inside it
(mounting it via a loop device). Each file is copied in blocks of fixed
size (a few KBs, I can't remember the exact figure now), so also files
as big as half the partition don't raise problems. Once all the files
are copied into the loop target filesystem, the blocks of the target
filesystem are remapped to their correct position in the partition,
effectively replacing the old filesystem. There is no need of a backup
for such operation, unless, of course, somewhat goes wrong...

Giovanni.
-- 
Giovanni Mascellani <mascellani@poisson.phc.unipi.it>
Pisa, Italy

Web: http://poisson.phc.unipi.it/~mascellani
Jabber: g.mascellani@jabber.org / giovanni@elabor.homelinux.org

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