# lvdisplay
  --- Logical volume ---
  LV Name                /dev/odin/root_1
  VG Name                odin
  ...
  LV Size                30.00 GB
  ...

Since my root partition is on LVM, I can do a snapshot to get a point-in-time view of the root partition even as the system is running and software is making changes to the filesystem. To create the snapshot:

lvcreate -L 30G -s -n root_1_snap /dev/odin/root_1

The arguments are: lvcreate -L {size} -n {snapshot name} {lvm device path}

Then, you do a dump backup:

# dump 0uf odin.0.img /dev/mapper/odin-root_1_snap
  DUMP: Date of this level 0 dump: Mon Apr 28 10:52:39 2008
  DUMP: Dumping /dev/mapper/odin-root_1_snap (an unlisted file system) to odin.0.img
  DUMP: Label: none
  DUMP: Writing 10 Kilobyte records
  DUMP: mapping (Pass I) [regular files]
  DUMP: mapping (Pass II) [directories]
  DUMP: estimated 3130770 blocks.
  DUMP: Volume 1 started with block 1 at: Mon Apr 28 10:52:46 2008
  DUMP: dumping (Pass III) [directories]
  DUMP: dumping (Pass IV) [regular files]
  DUMP: Closing odin.0.img
  DUMP: Volume 1 completed at: Mon Apr 28 10:55:49 2008
  DUMP: Volume 1 3120540 blocks (3047.40MB)
  DUMP: Volume 1 took 0:03:03
  DUMP: Volume 1 transfer rate: 17052 kB/s
  DUMP: 3120540 blocks (3047.40MB) on 1 volume(s)
  DUMP: finished in 182 seconds, throughput 17145 kBytes/sec
  DUMP: Date of this level 0 dump: Mon Apr 28 10:52:39 2008
  DUMP: Date this dump completed:  Mon Apr 28 10:55:49 2008
  DUMP: Average transfer rate: 17052 kB/s
  DUMP: DUMP IS DONE

The arguments are: dump {level}uf {output file} {source device path}

Next, remove the snapshot to keep from hogging LVM space:

  lvremove /dev/odin/root_1_snap
Do you really want to remove active logical volume "root_1_snap"? [y/n]: y
  Logical volume "root_1_snap" successfully removed

Optionally, compress the backup image for safekeeping.

gzip /backup/odin.0.img &

The ampersand (&) will make the process run in the background. By doing this, I saved 71.2% of the size, down to an image that was 878MB from 3050MB!

To restore from said backup, assuming you have a ready ext3 partition of the appropriate size: Uncompress it if need be:

gunzip /backup/odin.0.img.gz

Then:

cd / && rrestore rf /backup/odin.0.img