Mmm, there has been some discussion around this ..
Technically using cache=writeback "should" be safe for migration.
(which is the method I use)
So .. I need "cache=writeback" and "sharable" for migration to happen.
(the performance hit with cache=off is an unacceptable performance hit, at
least for me ..)
From the QEMU lists, 2012;
"In short, if you're using a recent kernel with ext3 or ext4, cache=writeback
is absolutely safe. If you're using an older version of ext3, cache=writeback
is still safe but ext3 itself isn't. cache=writeback can make the situation
worse."
...
--
Gareth Bult
“The odds of hitting your target go up dramatically when you aim at it.”
See the status of my current project at http://vdc-store.com
----- Original Message -----
From: "Stefan Kooman" <ste...@bit.nl>
To: "Javier Fontan" <jfon...@opennebula.org>
Cc: "Gareth Bult" <gar...@linux.co.uk>, users@lists.opennebula.org
Sent: Thursday, 30 January, 2014 2:38:23 PM
Subject: Re: [one-users] Setting the "SHAREABLE" attribute
Quoting Javier Fontan (jfon...@opennebula.org):
> I've been digging a bit more in the shareable issue and it seems that
> setting "shareable" to a disk just disables cache in qemu/kvm[1]:
>
> --8<------
> 4158 virBufferAsprintf(&opt, ",cache=%s", mode);
> 4159 } else if (disk->shared && !disk->readonly) {
> 4160 virBufferAddLit(&opt, ",cache=off");
> 4161 }
> ------>8--
>
> Isn't it enough to disable cache for disks that can be migrated?
Yes it is, at least in our environment (Ubuntu 13.10). Cache has to be
off (to avoid data loss while migrating vm).
/etc/one/vmm_exec/vmm_exec_kvm.conf:
DISK = [ driver = "raw" , cache = "none", io = "native"]
Gr. Stefan
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