[Box Backup] Backup the backup

Chris Wilson boxbackup at fluffy.co.uk
Wed Nov 1 14:51:04 GMT 2006

  This message is in MIME format.  The first part should be readable text,
  while the remaining parts are likely unreadable without MIME-aware tools.

Content-Type: TEXT/PLAIN; charset=utf-8; format=flowed
Content-Transfer-Encoding: QUOTED-PRINTABLE

Hi Simon,

On Wed, 1 Nov 2006, Simon Lundstr=F6m wrote:

> From man rsync:
> -u, --update                update only (don't overwrite newer files)
> I thought that was going to work, but maybe not?

I suspect that you will get a mixture of newer and older files on the=20
server, as soon as the client switches in the middle of an rsync process,=
which is guaranteed to happen eventually.

I also suspect that you may have problems with synchronisation of=20
directories between the two servers, but I can't put my finger on an exact=
failure mode right now. Go ahead and try it, but be extremely careful,=20
that would be my advice. Also, run bbstoreaccounts check on each account=20
regularly on both sides and watch out for errors.

> Maybe unison http://en.wikipedia.org/wiki/Unison_%28file_synchronizer%29=
> is the way to go?

Maybe, but I found it's unsuitable for automatic synchronisation due to=20
its tendency to develop conflicts in practice. For example, if you updated=
a file and a directory on one side, and the directory (but not the file)=20
on the other, you would get a conflict on the directory but not on the=20
file. But you can't just upload the file without overriding one version of=
the directory, otherwise the result is inconsistent (doesn't agree with=20
either side) and may be invalid.

> Because many of these companies are small and don't have a lot of=20
> bandwidth since they only surf and check their mail they can't only use=
> remote backup but needs local backup. (5-10 ppl transmitting 2-10GB over=
> 2Mbit can be come quite slow.

But they're only syncing changes and only when they're on the road, so I=20
don't think it would be so bad. Besides you would probably use exactly the=
same amount of bandwidth in the other direction (upload) to update the=20
secondary server, and upload bandwidth is more scarce than download=20
bandwidth. I suppose it depends on whether the clients are more usually on=
the road or in the office.

> I will only use lazy mode, i.e. backups will not be automatic. Besides=20
> not all clients can have servers or ports opened in their firewall.

You can get around the latter restriction by tunneling to your server=20
through the firewall.

Cheers, Chris.
_ ___ __     _
  / __/ / ,__(_)_  | Chris Wilson <0000 at qwirx.com> - Cambs UK |
/ (_/ ,\/ _/ /_ \ | Security/C/C++/Java/Perl/SQL/HTML Developer |
\ _/_/_/_//_/___/ | We are GNU-free your mind-and your software |

More information about the Boxbackup mailing list