Re: About network failures while uploading

[Colin Percival <cperciva@tarsnap.com>]

On 03/08/14 06:29, tarsnap wrote:
> Continuing a thread from Jul 2011, I would like to know if in case of
> backing up 1 file (>1 GB) and tarsnap quitting due to 'Too many network
> failures', parts of the file are retained on the server, and re-used
> when repeating the backup command in tarsnap.
> 
> I got the uncomfortable feeling that the error message I got: "Error
> closing archive", means 'NO'.

Probably.  There's a very slim chance that the final transaction commit
request got through to the server but your connection died before the
acknowledgement came back.

> Further I wonder why the backup fails already after 4 errors looking up
> betatest-server.tarsnap.com.

It's the other way around -- when a connection is failing, tarsnap will
retry several times before giving up; and as part of those retries it will
perform new DNS lookups (and warn when those fail due to your internet
connection being down).

> This way, with my quite unstable network
> connection, I'm afraid the uploading will never complete.

I'd recommend using the --checkpoint-bytes option with a fairly low
setting (e.g., --checkpoint-bytes 32M) so that you'll have lots of
checkpoints created.  That way when an archive fails you'll still have
the first section of the archive stored -- and that data can then be
used for deduplication purposes when you create another archive, which
will make future archives use less bandwidth and complete faster.

Of course, finding an internet connection which doesn't break for 5
minutes at a time would be ideal.  (5 minutes is how long tarsnap will
keep on trying to reconnect.)

-- 
Colin Percival
Security Officer Emeritus, FreeBSD | The power to serve
Founder, Tarsnap | www.tarsnap.com | Online backups for the truly paranoid