Re: New data reported too big

[Colin Percival <cperciva@tarsnap.com>]

On 09/29/13 06:26, Yonatan Broza wrote:
> I'm using tarsnap to backup around 22GB in 22K files.
> 
> There's hardly any difference between backups (verified using diff) yet tarsnap
> reports 12MB of new data.
> 
> Most timestamps are changed since most of the files are recreated before each
> backup.
> 
> What's the reason for the large amount of new data?

Tarsnap stores a 512-byte tar header for each file, and this header includes the
file modification time.  22,000 files x 512 bytes/file = 11.2 MB, so this looks
like the reason for the new data you're seeing.

The good news is that tar headers tend to compress very well, so the data you're
actually uploading -- the *compressed* new data -- is almost certainly much less
than that.

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