Re: [rdiff-backup-users] Moving the backup-location to another machine

[Ron Leach]

On 12/01/2014 12:15, Chris Wilson wrote:
> total != used+available because some blocks are reserved for use by
> administrators (the root user) by the filesystem.
>
> [snip]
> The number of reserved blocks is:
>
> * Old system: 1894289664 - 1874215424 - 20074240 = 0
> * New system: 1922726712 - 1825057796 - 4 = 97668912, or 5% of total
>
> It seems that someone reduced the number of reserved blocks on your
> old system to zero.

That was set by the Debian installer, in fact, but it was xfs, though, 
not ext4.  This new lv is ext4.

> It's an extremely bad idea in my view to run an ext4 filesystem over
> 80% full, as it results in increasing fragmentation over time and
> there is no defragmentation tool available.

Very interesting point.  We keep the backup increments indefinitely 
so, other than rdiff-backup housekeeping files, the bulk of the 
filesystem stays in existence.  No deletion, in practice.  I'm not 
sure if the reverse-diffs change on each backup run, or whether 
additional new reverse diffs are created each time any source files 
(our main, and user, files etc) for the backup alter.

I'm going to check whether xfs does things differently - I am very 
anxious to move this archive.  The lv only exists for backup 
destination and, since our existing backup failed to copy onto the lv, 
I can start again and put a different filesystem on it.

Chris, that was an extremely helpful post; it has pointed me towards a 
more critical appraising of suitable filesystems.

Ron