Re: tar -c -G -N <date> query

[Stepan Kasal]

Hi again,

On Fri, Jul 18, 2003 at 09:50:12PM +0100, Tom Crane wrote:
> > > One question: Can I fabricate a snapshotfile? The format appear to be
> > > device_number directory-inode-number directory-spec
> Just checked it. It does work, the mapping is device_number = major_id*256 + 
> minor_id

good.

> I did wonder about that... but it seemed too nasty to be true --  I mean 
> to tie the tarfile to the H/W-particulars rather than the mount-point for 
> example. I've not tried it but I wonder if this means that a tarfile
> created with listed-incremental could not be extracted on to a different
> IDE HD partition, or a device on a different bus altogether. Surely this
> can't be true...? ;-| 

It really isn't true.  The device numbers are stored in the snapshot file
only.  That means they are used in order to determine whether the file is
the same as during the previous backup.  If you move part of your
filesystem and mount it from another place, that part will be fully
backuped by the following incremental backup.
Incremental backup should be used to keep track of small differences
on a stable system.  If you reorganize your fstab, you should probably
start with another full backup.  (Or you can change the device number
in the snapshot file.  ;-)

You don't need the snapshot file to unpack the backup, you only need it
if you want to make next incremental backup, relative to the previous one.

Hope this clarifies it.

Cheers,
        Stepan Kasal

> Ps. CCed: address@hidden

I too.