[pve-devel] qemu-server: add directsync cache mode

[Alexandre DERUMIER]

> I do not really understand that. If someone does not sync the data is at risk, yes. 

It's works the same way than writethrough, but bypass host cache.

It's do a fsync on each write to be sure to not loose a single transaction.
could be usefull for database by exemple, where we don't have to use host cache.


Also,some older linux (or "old" filesystem, could corrupt with cache="none" or cache"writeback",
as they dont send flush command.


some infos:
http://lists.fedoraproject.org/pipermail/virt/2011-October/002956.html


>> But why do we want to have a workaround for that? 
I just want to add all cache mode available in qemu. Maybe some users want it .


If I have time, I think i'll write a wiki article about cache options, as it's not simple to understand how they works.


----- Mail original ----- 

De: "Dietmar Maurer" <dietmar at proxmox.com> 
À: "Alexandre Derumier" <aderumier at odiso.com>, pve-devel at pve.proxmox.com 
Envoyé: Mardi 10 Avril 2012 06:10:29 
Objet: RE: [pve-devel] qemu-server: add directsync cache mode 

> This mode is useful when guests may not be sending flushes when appropriate 
> and therefore leave data at risk in case of power failure. 

I do not really understand that. If someone does not sync the data is at risk, yes. 
But why do we want to have a workaround for that? 

- Dietmar 




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