[gentoo-user] Re: snackup

[Alex Schuster]

covici@××××××××××.com writes:

> I have a question -- where would lvm put a snapshot and how could I
> pass some list of excludes to rdiff-backup.  I have an lvm which is
> taking all the PEs and a snapshot would take up lots of disk space --
> or would it.  Would I need some free pes to put the snapshot?

An LVM snapshot has to be in the same volume group as the LVM. If all your 
physical extends are full, this will not work I'm afraid.
But you can reduce the size of one LVM with lvreduce. Of course you have 
to resize the file system inside first. This is a little more complicated 
than extending the size, because you have to specify the size when 
reducing the file system and the LVM. And the file system has to be 
unmounted :(

Let's say you want to reduce your data partition of 15G to 10G:

  umount /dev/myvg/data
  fsck -f /dev/myvg/data
  resize2fs /dev/myvg/data 9G
  lvresize -L 10G /dev/myvg/data
  resize2fs /dev/myvg/data
  mount /dev/myvg/data
 
The 2nd resize2fs maximizes the size of the fs inside the LVM. I do not 
know (does anyone else?) if you could skip this and reduce it to 10G in 
the first resize2fs step. Just to be on the safe side I reduce it a little 
more, and let it adapt do the reduced LVM size afterwards.

The snapshot itself takes nearly no space at all - it only keeps the 
changes that occur in the LVM while the snapshot is in place. So it grows 
when you modify the LVM you snapshotted. When you do not much 
modifications, 15-20% is enough according to the lvcreate man page. And I 
think I had it much lower without problems. I would expect that it can be 
really small when you do not change the original LVm much. snackup uses 2G 
as default, change this with option -s. Of course, when you do large 
modifications, like creating larger files, this may be too small.

Excludes can be given with the -x option (multiple times). And have a look 
at the config template that snackup -T gives you. Near the bottom, the 
variable oXclude is defined. It is an array, just change it to your needs. 
it already excludes things like ccache, kdecache-* directories, 
*/tmp/portage, and the dreaded nepomuk directory fo KDE4 because this 
sometimes gets really REALLY large here.

snackup -x dip -x dap would exclude the stuff already pre-defined and dip 
and dap. If you want to exclude dip and dap only, call snackup -x "" -x 
dip -x dap. But I find it easier to adapt the oXclude array.

	Wonko