[pve-devel] [PATCH qemu-server] qemu-img convert: use cache=none

Alexandre DERUMIER aderumier at odiso.com
Mon Mar 26 09:39:13 CEST 2018


>>is writeback+direct instead, so I don't think this should affect rbd.

Does qemu-img mirror really send the flush with writeback ?


for ceph, by default:

"rbd cache writethrough until flush = true"


and we have a patch for rbd driver

https://git.proxmox.com/?p=pve-qemu.git;a=blob;f=debian/patches/pve/0018-block-rbd-disable-rbd_cache_writethrough_until_flush.patch;h=e75da3c6cf820999d1b696ddac6d63a61f8a529f;hb=HEAD


which said : if cache=unsafe, "rbd cache writethrough until flush=false"



(I need to dig in pve-devel mailing, I think we have already talk about this 1 or 2 years ago)


----- Mail original -----
De: "Fabian Grünbichler" <f.gruenbichler at proxmox.com>
À: "pve-devel" <pve-devel at pve.proxmox.com>
Envoyé: Lundi 26 Mars 2018 08:42:14
Objet: Re: [pve-devel] [PATCH qemu-server] qemu-img convert: use cache=none

On Fri, Mar 23, 2018 at 04:45:11PM +0100, Alexandre DERUMIER wrote: 
> any impact on ceph rbd ? (as writeback help a lot with sequential writes on ceph) 

the default for convert is 'unsafe', which is writeback+no-flush. 'none' 
is writeback+direct instead, so I don't think this should affect rbd. 

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