John Hudak wrote:
> Hello:
> I am considering using an external USB drive as the storage for my backups.
> I am running backup pc under Debian 5.0.
> Part 1
> What do I need to do to configure the USB disk as the target? (e.g. how
> do I do it?)
With packaged backuppc installs you need to make your mount point were backuppc
expects it - which would be /var/lib/backuppc. If you are starting from
scratch, you could make that directory and mount the drive before installing.
Otherwise follow the directions on the wiki for moving the archive.
> The USB disk is currently formatted as a NTFS file system. Do I *need*
> to reformat it to ext3? or other?
Yes. The filesystem must permit hardlinks.
> Part 2
> Assume I am crazy paranoid about preserving backup data and I get a
> second USB drive to serve as a backup to the first USB drive.
> Also assume that I am not concerned about the bandwidth across the
> network or the various buses.
That's not crazy paranoid, that just approaching reasonable. Crazy paranoid is
making a 3-member raid1 mirror with the 3rd being the external drive position
that is periodically swapped - so you always have 2 internal, 2 external copies
with 1 always offsite.
> From a data reliability standpoint, is it better to run a backup
> session to USB drive 1, and then repeat the backup to USB drive 2? OR
> run a backup session to USB drive 1, and then copy the backup
> directories to USB drive 2???
With just 2, I'd set them up identically and let the backup runs catch up when
you swap.
> The first approach could have errors in different backed up files on
> disk 1 or 2 but given the odds, very unlikely that the same exact error
> would show up
> in the same exact way in the same file across both USB disks.
> OTOH, the second approach would allow the exact error in the backup on
> USB disk 1 to be copied to USB disk 2.
They will both accumulate the same history and correct any errors in the
subsequent runs either with rsync comparisons or pool mismatches.
> I am leaning towards repeating the backup on two drives.
If you are paranoid you won't want to ever have both copies in the same place -
which might be easier to arrange with 3 of them.
> My understanding is that files that are backed up (using either rsync or
> smb) are 'encrypted' (for lack of a better word), and to view them I
> need to use zcat.-True?
Compressed is a better word - and the normal way to view them is through the
web
interface that takes care of the details. If you really anticipate needing to
restore elsewhere from your external drive you should build a suitable backuppc
system to make it fast and easy. Vmware on a laptop will work and vmware
player
(the 2.x versions) is pretty good about passing USB to the guest OS.
> Also, can the backup profile be specified to perform complete data
> copies periodically, as opposed to a baseline and then periodic
> incrementals?
You can specify the intervals for fulls/incrementals, but if you use rsync even
the fulls don't have to copy existing files.
> Lastly, does anyone have a statistical number that represents the
> probability of a backup file (e.g. on the target backup disk) containing
> an error introduced
> by the backup procedure?
Zero is a close approximation if you don't count files that are being modified
while you copy them.
> I know there are error probabilities for both
> disk and tape reads/writes failures, but am wondering if anything like
> that exists for the backup software.
Look for research on TCP errors. And the rsync algorithm if you use that.
> (A group I used to work with did
> this sort of testing, and actually had some statistics on the
> reliability of backup programs, wrt types of files, sizes, w/wo
> compression, and the types of compression. Not sure the open source
> community would go through this type of assessment - but thought I'd ask.
> Thanks for your help
I've always trusted rsync as much as anything to both create exact copies and
detect differences. It's at least in the same realm of reliability as the
storage media and OS that it works over - and better than your external USB
drives.
--
Les Mikesell
lesmikesell AT gmail DOT com
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