[pve-devel] Speed up PVE Backup

Eneko Lacunza elacunza at binovo.es
Tue Jul 26 10:13:59 CEST 2016


Hi,

El 26/07/16 a las 10:04, Alexandre DERUMIER escribió:
>>> I think qmrestore isn't issuing any flush request (until maybe the end),
> Need to be checked! (but if I think we open restore block storage with writeback, so I hope we send flush)
>
>>> so for ceph storage backend we should set
>>> rbd_cache_writethrough_until_flush=false for better performance.
> I think it's possible to pass theses flag in qemu block driver option, when opening the rbd storage
>
>
> http://docs.ceph.com/docs/hammer/rbd/qemu-rbd/
>
> qemu-img {command} [options] rbd:{pool-name}/{image-name}[@snapshot-name][:option1=value1][:option2=value2...]
>
>
> for qemu-img or with qemu drive option, I think it's possible to send as option, ":rbd_cache_writethrough_until_flush=false"
I developed a small patch to do this, waiting to test it in our setup 
(today or tomorrow)
> But if missing flush if really the problem, it should be added to restore command directly. (maybe 1 flush each 4MB for example)
This flush is needed only for Ceph RBD, so I think using the flag above 
would be more correct.

There is no reason to flush a restored disk until just the end, really. 
Issuing flushes every x MB could hurt other storages without need.

In fact all this is because Ceph trying to "fix" broken virtio drivers... :)

Thanks
Eneko

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