[plug] backup script

[Craig Ringer]

 > I would have imagined it'd be intertwined generically with the VFS layer
> (or Linux equiv). But if Linux waits for the disk to finish (or, rather,
> for the disk to lie about finishing), then perhaps it's only a practical
> concern if you're planning on doing something physical with the drive,
> e.g. powering it down or something weird like that :-)

Indeed. The reason I'm syncing before taking the snapshot is that I'm 
attmpting to make sure that incomplete FS transactions make it to the 
disk. A reiser filesystem with incomplete transactions cannot be mounted 
off read-only media like an LVM snapshot, as it wants to replay the 
transactions. I'd love a command simiar to xfs's xfs_stop (?) to tell 
the FS to finish up then delay all writes until told to continue -  but 
there doesn't seem to be one for reiser.

I've found that syncing does make a big difference - I still have the 
odd bad snapshot, but it's not common. The "bad" snapshots are OK, of 
course, if restored to a r/w medium - they just can't be mounted directly.

As for where it happens, you're probably right - it'll be the VFS layer. 
Maybe 2.4 doesn't require multiple syncs anymore - but I'll do it to be 
sure.

Craig Ringer

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