Xen users - Aug 2009 - Exploring Xen 3.3.2 with LVM, iSCSI and PVSCSI...

Hi Fellas!
 I''m trying to explore the possibilities of PVSCSI, as for example,
online
resize, look:

At the Debian Lenny dom0 with Xen 3.3.2 and Linux 2.6.18 compiled from
xen.org:

1) lvcreate -L 10G -n guest01-root HyperVG01;
2) configure the guest01 PV domU with PVSCSI using HyperVG01/guest01-root as
partition, not as virtual disk;
3) start guest01;
4) lvextend -L +15G HyperVG01/guest01-root.

 Should I need to reboot the domU to be able to use this +15G? Or the resize
is online?!

 If yes, the resize can be done online, what happens if I put the iSCSI
target/client between the LVM and PVSCSI, the online resize will still be
available?

Thanks!

-
Thiago


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Thiago Camargo Martins Cordeiro wrote:
>  I''m trying to explore the possibilities of PVSCSI, as for
example,
>online resize, look:
>
>At the Debian Lenny dom0 with Xen 3.3.2 and Linux 2.6.18 compiled 
>from xen.org:
>
>1) lvcreate -L 10G -n guest01-root HyperVG01;
>2) configure the guest01 PV domU with PVSCSI using 
>HyperVG01/guest01-root as partition, not as virtual disk;
>3) start guest01;
>4) lvextend -L +15G HyperVG01/guest01-root.
>
>  Should I need to reboot the domU to be able to use this +15G? Or 
>the resize is online?!
As far as I know, the new size will not get passed to the client. A 
reboot is not sufficient, I think you need to shutdown and recreate 
the client. There are xm commands to dettach and attach storage 
volumes from the guest, so if you are able to unmount the volume in 
the guest then this may be a means of doing a resize without a reboot 
- I haven''t used these commands.
>  If yes, the resize can be done online, what happens if I put the 
>iSCSI target/client between the LVM and PVSCSI, the online resize 
>will still be available?
You mean, share the volume form Dom0 with iSCSI and mount it in the 
guest as an iSCSI volume ? I think you''ll find performance is poor. 
I''ve tried mounting an iSCSI volume in a guest (from an external 
device, not Dom0) and performance was very poor - I believe due to 
the single thread nature of Dom0 networking. I suspect the same issue 
would apply if the volume was being exported from Dom0.

In my case, I mounted the iSCSI volume in Dom0 and passed it to the 
guest as a normal physical volume. Not my preferred option as it 
makes migration harder, but performance is good.

But with iSCSI, you can do an online resize, but you still need to 
unmount the filesystem in the guest before you can resize it.

-- 
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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