[pve-devel] Speed up PVE Backup

[Alexandre DERUMIER]

>>Ceph drops it's own readahead cache after the first 50MB to let the OS 
>>do his own readahead which makes sense. But qemu itself does not have 
it'>>s own readahead while doing backups. 

Does is help (for backup) if you always force readahead with 

rbd readahead disable after bytes=0



----- Mail original -----
De: "Stefan Priebe" <s.priebe at profihost.ag>
À: "dietmar" <dietmar at proxmox.com>, "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Jeudi 18 Février 2016 21:26:13
Objet: Re: [pve-devel] Speed up PVE Backup

Hello Dietmar, 
Am 16.02.2016 um 14:55 schrieb Stefan Priebe - Profihost AG: 
> Am 16.02.2016 um 12:58 schrieb Stefan Priebe - Profihost AG: 
>> Am 16.02.2016 um 11:55 schrieb Dietmar Maurer: 
>>>> Is it enough to just change these: 
>>> 
>>> The whole backup algorithm is based on 64KB blocksize, so it 
>>> is not trivial (or impossible?) to change that. 
>>> 

Regarding readahead - you mentioned it earlier - this is not working 
with ceph and qemu backup. 

Ceph drops it's own readahead cache after the first 50MB to let the OS 
do his own readahead which makes sense. But qemu itself does not have 
it's own readahead while doing backups. 

Any reason to use 64k blocks and not something bigger? Backups should be 
sequential on all storage backends so something bigger shouldn't hurt. 

Greets, 
Stefan 
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