Re: [BackupPC-users] Full backups are slower

[Holger P. <wb...@pa...>]

Hi,

dan wrote on 29.10.2007 at 07:51:46 [Re: [BackupPC-users] Full backups are slower]:
> On 10/29/07, Nils Breunese (Lemonbit) <ni...@le...> wrote:
> > Toni Van Remortel wrote:
> > > Although I use rsync for all backups, full backups are generally
> > > slower than incremental backups (up to 5 times).

full backups are, well, what we expect backups to be: make an exact copy of
living data. Incremental backups are a speedup at the cost of not always
getting everything exactly right: faster, cheaper, within an acceptable
margin of error.

> > > What can be the cause?

The speedup works as expected?

> actually, the simple truth is that a full rsync rescans every single file
> while an incremental only scans for files that have changes.

Make that "obvious changes". That is the margin of error: the changes that
are not obvious enough for rsync to detect.

> it just takes more time to look at every file vs ashort list.

And it puts more wear on your disks, and it takes slightly more bandwidth
for exchanging checksums for possibly a great number of files which would
otherwise be ignored. If it wasn't for the advantage of gaining something,
why would you do incremental backups in the first place?

In fact, if disk and CPU speeds rather than network bandwidth are your
bottleneck, rsync backups may not be much faster than tar backups.

Regards,
Holger