Re: [Xen-users] Performance of network block devices (iSCSI)

[Simon Hobson <linux@xxxxxxxxxxxxxxxx>]

On 14/11/08, Javier Guerra wrote:
> On Thu, Nov 13, 2008 at 5:58 PM, Simon Hobson <linux@xxxxxxxxxxxxxxxx> wrote:
> >  I've deliberately not put the iSCSI initiator in Dom0 as I want to run the
> >  absolute minimum in Dom0. Also, putting the iSCSI initiator in Dom0 makes it
> >  harder to move a VM to another host - having it in the DomU means that the
> >  VM can be moved without any config changes.
> you should really try that.  the different nature of net- and
> block-devices means that there are a lot less context switches per MB
> transferred, and the point of acknowledging makes a huge difference in
> latency sensibility.
OK, I've *finally* managed to scrounge another box to do some testing 
on. I've setup open-iscsi in Dom0 and performance seems to be a lot 
better - I'm getting about 20MB/s and the backup server isn't sat on 
99% wio :-)

I have another question though ...

on this page http://wiki.debian.org/iSCSI/open-iscsi it says :
> You can then mount the new device, but under most situation, you 
> will want to use LABEL= syntax in /etc/fstab (see e2label).
I assume this is because the device name can change across restarts. 
Since I'm not mounting the volume in Dom0, just passing it to the 
guest in a "disk = [ 'phy:v ..." line, any suggestions on the best 
way to deal with this ?

--
Simon Hobson

Visit http://www.magpiesnestpublishing.co.uk/ for books by acclaimed
author Gladys Hobson. Novels - poetry - short stories - ideal as
Christmas stocking fillers. Some available as e-books.

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