Re: [PATCH] qemu: use statically allocate 512 byte buffer in the stack for sector in bdrv_commit

[Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org>]

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Le lundi 07 janvier 2008 à 10:34 -0500, Javier Guerra a écrit :
> On 1/7/08, Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org> wrote:
> > What I'm wondering now is: is it really useful to have "cache=off" and
> > "snapshot=on" at the same time ?
> 
> does "cache=off" means disk cache? if so, it might be useful to test
> clustering filesystems.

"cache=off" means files is opened with "O_DIRECT" and thus there is no
cache in the kernel memory on the host side.
IMO, "cache=off" and "snapshot=on" are incompatible because a snapshot
can be seen like a cache.

> so far, the only way is to setup a network block device (iSCSI, AoE,
> nbd). i'd like to simply specify the same backing file for two
> instances' hdb parameter.

I'm sorry but I don't understand this part.

> and snapshots help a lot to go back after blowing up the on-disk structures

But I think if you use a snapshot there is no reason to use "cache=off"

Laurent
-- 
----------------- Laurent.Vivier-6ktuUTfB/bM@public.gmane.org  ------------------
  "La perfection est atteinte non quand il ne reste rien à
ajouter mais quand il ne reste rien à enlever." Saint Exupéry

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