Re: resuming backups

[Colin Percival <cperciva@tarsnap.com>]

On 07/07/10 05:45, Michael Stevens wrote:
> Question I've been wondering about: I want to backup a lot of data from
> a machine with a slow and sometimes unreliable net connection. So I may
> lose the net connection while backups are being created, especially the
> initial one.
> 
> Is there a sensible way to resume an incomplete backup?

No.  Tarsnap doesn't do that.  What you want to do instead is keep the
incomplete backup as a partial archive, then create a new (complete) archive.

Partial archives can be created in a number of ways, but the approach which
matters in this context (unreliable network connectivity) is checkpointing
using the --checkpoint-bytes option (as Johan Brinch pointed out).  This will
ensure that if/when your backup job dies due to a lack of network connectivity
the progress (up to the last checkpoint) will be saved as a partial archive.

When you subsequently create a new archive, Tarsnap will recognize when data
it is processing is identical to previously-uploaded data -- including data in
the checkpointed archive -- and will only upload the new data.

-- 
Colin Percival
Security Officer, FreeBSD | freebsd.org | The power to serve
Founder / author, Tarsnap | tarsnap.com | Online backups for the truly paranoid