Hi,

Adam Goryachev wrote on 15.06.2007 at 11:28:13 [Re: [BackupPC-users] How to 
move backuppc data from lvm to bigger disks/lvm?]:
> Ralf Gross wrote:
> > [...]
> > dd if=/dev/mapper/VolGroup00-LogVol00 bs=8192 of=backuppc.dump
> > [...]
> > I think the dd data includes information about the lvm volume/logical
> > groups.
> [...]
> The problem I see in your suggestion is that you are copying a 1TB
> filesystem/partition into a 800GB one therefore if you have stored data
> at the end of the drive, then it will be lost, the above should solve
> that problem.

just to make it clearer:
the device file name /dev/mapper/VolGroup00-LogVol00 means you have not been
very imaginative when choosing VG and LV names, but aside from that, it
represents a plain block device. The filesystem is not and should not be
aware of how the underlying block device is implemented. Reading
/dev/mapper/VolGroup00-LogVol00 gives you the concatenation of the raw
blocks it consists of in ascending order, just like reading /dev/sda1,
/dev/sda, /dev/fd0 or /dev/sr0 does (/dev/sr0 is likely not writable though)
- nothing more and nothing less. Meta-information about VG and LVs is
stored in the PVs outside the data allocated to any LV.

I agree that you will need at least as much space as your LV takes up if you
want to copy it. I would add that copying into a file will probably give you
more trouble than copying to a block device (provided it is large enough).
There's simply one layer less of arbitrary file size limits you would be
dealing with.

Regards,
Holger

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