Re: [rdiff-backup-users] rdiff-backup versus rsnapshot

[Chris Wilson]

Hi all,

On Mon, 28 Apr 2008, Mike Marseglia wrote:

> A quick google turned up the following from
> http://www.backupcentral.com/components/com_mambowiki/index.php/Rdiff-backup:
...
> Disadvantages
> 
> Let’s be honest: rdiff-backup has some disadvantages too:
> 
> Speed
> 
>     rdiff-backup consumes more CPU than rsync and is therefore slower than
> most rsync scripts. This difference is often not noticeable when the
> bottleneck is the network or a disk drive but can be significant for
> local backups.

I would add the following:

rdiff-backup uses a lot more network bandwidth than rsync. About 1GB per 
100GB covered per backup, in my estimate, in addition to the deltas. This 
makes it too slow for us to use for daily offsite backups (uploading over 
a 384kbit DSL, backing up about 500GB daily).

rdiff-backup is a bit fragile. It's easy to corrupt the metadata, for 
example if the store disk gets full, or multiple backups run to the same 
destination at the same time, and usually impossible (i.e. nobody knows 
how) to recover the history after that happens.

rdiff-backup does not allow one to remove an intermediate increment (for 
example if a large file accidentally got backed up that shouldn't be) or 
to remove a subtree of the backup (at least not without risking metadata 
corruption again).

>     With rsync scripts, all past backups appear as copies and are thus 
> easy to verify, restore, and delete. With rdiff-backup, only the current 
> backup appears as a true copy. (Earlier backups are stored as compressed 
> deltas.)

For me, this is a mixed blessing. Large numbers of small files take a lot 
of space on the remote server (as with rsync too), and you can trash your 
backup by accidentally modifying files in the remote repository. But it 
has been useful in emergency recovery situations where I have had to boot 
from a recovery CD that didn't have rdiff-backup on it.

I do like rdiff-backup and I use it extensively, but these are things that 
I wish for that would make it even better.

Cheers, Chris.
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