Thanks all for your answers.
I'm getting back on this issue. Let me be more specific :
I have 1 remote server which is my production Zimbra. Let's call it "server"
The install is standard, and I'm running ZCS 6.0.6 at the moment. I have around 30 accounts.
I also have an "office" server, which I can access physically. Let's call it "backup"
What I want to do is just replicate the content of
server:/opt/zimbra/backup
to
backup:/backups/zimbra/backup
So inside of those dir, I would have the same tree :
accounts.xml sessions tmp
And inside backup:/backups/zimbra/sessions, I want to have all full and incr backups, i.e. those on server:/opt/zimbra/backup/sessions + those which have been deleted over time.
Currently, I'm using :
on "backup" :
rsync -aHvz server:/opt/zimbra/backup /backups/zimbra
Now, maybe I'm just reading wrong info from df and du commands, but those backups are really taking a lot of diskspace :
Code:
root@server:/opt/zimbra/backup/sessions# du -hs *
22G full-20100604.230010.263
612K full-20100610.230034.511
23G full-20100611.230008.043
23G full-20100618.230010.257
620K full-20100623.230039.677
23G full-20100625.230010.855
89M incr-20100531.230011.174
58M incr-20100601.230010.711
109M incr-20100602.230012.958
63M incr-20100603.230009.654
62M incr-20100605.230011.670
8.0M incr-20100606.230011.065
55M incr-20100607.230012.156
111M incr-20100608.230011.642
78M incr-20100609.230009.626
64M incr-20100610.230010.017
51M incr-20100612.230017.684
25M incr-20100613.230010.515
106M incr-20100614.230011.702
54M incr-20100615.230017.320
94M incr-20100616.230015.921
113M incr-20100617.230010.885
218M incr-20100619.230014.408
15M incr-20100620.230010.343
119M incr-20100621.230014.579
85M incr-20100622.230016.570
81M incr-20100623.230012.822
198M incr-20100624.230010.893
108M incr-20100626.230014.666
9.8M incr-20100627.230010.251
221M incr-20100628.230011.867
182M incr-20100629.230009.865
298M incr-20100630.230011.408
root@server:/opt/zimbra/backup/sessions# df -kh
Filesystem Size Used Avail Use% Mounted on
[...]
/dev/md1 412G 124G 268G 32% /opt
root@server:/opt/zimbra/backup/sessions# du -hs /opt/zimbra
123G /opt/zimbra
There's almost only zimbra in /opt (rest is less than 1GB).
Why are those backups taking so much space ?
Over a year, it will eat 50*20GB, more than 1 TB of backups, just for less than 30 ppl ? Sounds a bit much.
I also recall seeing some 1 or 2 GB full backups a few month ago. Maybe using the wrong command ?
Anyway, as you can see, I'm loosing control over the situation (as I nearly have no more space left on my "backup" machine), so if you think I did something wrong, just tell me. For the record, I've got less than 1 year of experience on Zimbra, and my time is not fully going to it 
Thanks !