[one-users] Setting the "SHAREABLE" attribute

[Javier Fontan]

I'll investigate a bit more on this issue but from the qemu driver
code it seems that cache is disabled with shareable flag.

On Thu, Jan 30, 2014 at 4:07 PM, Gareth Bult <gareth at linux.co.uk> wrote:
> 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" <stefan at bit.nl>
> To: "Javier Fontan" <jfontan at opennebula.org>
> Cc: "Gareth Bult" <gareth at linux.co.uk>, users at lists.opennebula.org
> Sent: Thursday, 30 January, 2014 2:38:23 PM
> Subject: Re: [one-users] Setting the "SHAREABLE" attribute
>
> Quoting Javier Fontan (jfontan at 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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-- 
Javier Fontán Muiños
Developer
OpenNebula - The Open Source Toolkit for Data Center Virtualization
www.OpenNebula.org | @OpenNebula | github.com/jfontan