Re: [BackupPC-users] rsync: incremental vs. full backups

Disclaimer: I think I know what I'm talking about, but I'm not 100%.
I'm sure the experts here will correct me if I'm wrong.

On Wed, Jun 20, 2012 at 10:17 AM, jonas <jonas AT freesources DOT org> wrote:
> Now BackupPC has a full backup of all clients. Unfortunately it starts
> with full backups again as the first ones are older than seven days. But
> I really wonder about the time, BackupPC takes for doing the second
> round of full backups. I tought that only changed files were transfered
> when using rsync. And the stats look like I'm right. But still, full
> backups take up to two days, even if only a few new files are
> transmitted. Given that BackupPC still does a lot of parallel backups,
> maybe reading the list of files with rsync takes that long, even if I
> don't believe it.

The main (but not only for rsync) difference between full and
incremental backups are incremental backups are purely based on file
modification date[1].

The likely reason your subsequent fulls take so long is each file is
checksumed to see if it's changed. Network utilization will be lower
so the backup speed is limited by how fast the client can calculate
the checksums. I think newer versions of BackupPC do this by default
now but you can speed up rsync fulls using a checksum seed[2]

> Did I get anything wrong? I'm curious to hear your opinions.

Nothing wrong, but perhaps you need to tweak your full/incremental
intervals or allow more simultaneous backups if your server can handle
it.

Richard

[1] http://backuppc.sourceforge.net/faq/BackupPC.html#backup_basics
[2] http://backuppc.sourceforge.net/faq/BackupPC.html#rsync_checksum_caching

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