[PVE-User] WG: difference b/w backup types

Alain Péan alain.pean at lpp.polytechnique.fr
Wed Sep 28 17:36:36 CEST 2011

Le 28/09/2011 17:30, Matthew Caron a écrit :
> On 09/28/2011 11:21 AM, Alain Péan wrote:
>> Hi Jeremiah,
>> Just a question, just to know what is the best policy. Do you use
>> BackupPC to backup the image files inside the host, or the files inside
>> the VM ? The image files are big files, that change at least slightly
>> (logs, updates...), so backupPC needs to backup the whole (big) file
>> each time.
> Not necessarily. BackupPC uses rsync, which has a differential changes 
> algorithm, so it only sends the regions of the files which changed 
> over the wire. From the manpage:
> ===
> It is famous  for  its delta-transfer  algorithm,  which  reduces the 
> amount of data sent over the network by sending only the differences 
> between  the  source  files and  the  existing  files in the destination.
> ===
> As long as you're not moving the original files, off of the 
> destination (say, for offsite backups), this will only copy what changed.
> Of course, if you want offsites, you can set up a RAID 1 mirror on 
> your backup server, then pop the drive out in the morning, replace it, 
> and let it rebuild, then take the one you just pulled out offsite. Of 
> course, in this case I'd recommend a 3 way mirror, so that you still 
> have redundancy while the third disk is rebuilding.

Hi Matthew,

Thanks for your answer. You are right, rsync should copy only the 
difference. As I use BackupPC (but to backup the files inside PCs or 
VMs), I will give it a try on one VM.

Thanks again.

Alain Péan - LPP/CNRS
Administrateur Système/Réseau
Laboratoire de Physique des Plasmas - UMR 7648
Observatoire de Saint-Maur
4, av de Neptune, Bat. A
94100 Saint-Maur des Fossés
Tel : 01-45-11-42-39 - Fax : 01-48-89-44-33

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