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>]

[-- Attachment #1.1: Type: text/plain, Size: 2000 bytes --]

Well, in fact, I think you can't use snapshot with cluster filesystem:
as each qemu instance will write in its own snapshot and will not see
modifications made by other, and I don't think there is currently a way
to share snapshot between qemu instances.

Laurent

Le lundi 07 janvier 2008 à 11:42 -0500, Javier Guerra a écrit :
> On 1/7/08, Laurent Vivier <Laurent.Vivier-6ktuUTfB/bM@public.gmane.org> wrote:
> > Le lundi 07 janvier 2008 à 11:03 -0500, Javier Guerra a écrit :
> > > hopefully, it would now work with "-cache=off", don't you think?
> >
> > Well, I don't think the problem is at the host level but at the guest
> > level, because both instances of qemu share the host cache and thus
> > first instance should see changes made by the second instance (and
> > vice-versa).
> 
> that's what a cluster filesystem is designed to cope with (and in fact expects)
> 
> > There are also some caches at qemu level to emulate DMA, for instance in
> > hw/ide.c it is MAX_MULT_SECTORS (16) which is 8 kB buffer, perhaps your
> > problem is here but "cache=off" doesn't remove this.
> > Did you try to change MAX_MULT_SECTORS to 1 ?
> 
> nope, don't know enough of qemu internals...
> 
> but if those caches can be flushed from the guest, the filesystem
> should do that when writing its metadata
> 
> > What do you call a "cluster filesystem" ?
> 
> GFS, OCFS2, etc.   that is, filesystems that are designed to run on
> more than one host with shared block storage.  usually that means
> FibreChannel or iSCSI, but on VMs, a common backing could work too (at
> least in theory).
> 
> Xen manages it, at least on paravirtualized guests; hadn't tried on
> HVM guests. maybe the IDE-like emulation is too poor an interface to
> handle it.
> 
-- 
----------------- 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

[-- Attachment #1.2: Ceci est une partie de message numériquement signée --]
[-- Type: application/pgp-signature, Size: 189 bytes --]

[-- Attachment #2: Type: text/plain, Size: 278 bytes --]

-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace

[-- Attachment #3: Type: text/plain, Size: 186 bytes --]

_______________________________________________
kvm-devel mailing list
kvm-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org
https://lists.sourceforge.net/lists/listinfo/kvm-devel