Xen users - Nov 2007 - How to manage images/partitions for xen DomUs?

Hello,
I am trying to figure out the best way, how to configure a small cluster
with xen and High Availability (Heartbeat). I have two servers and a few
virtual machines. What I need is to ensure, that images or partitions of
the machines will be mirrored between the two nodes (maybe with drbd?).
But that is not all - I also need to enlarge the disks (because of
growing databases) of virtual machines sometimes (if it could be done
without shutting the machines down, it would be perfect!), so I am
thinking about some evms/lvm setup. But I have no idea how to configure
such a thing - how would it look like? Do you have any ideas, schematics
or something? Like layered model - should I use evms to group drbd
devices in domain 0 or lvm in virtual machines to group virtual disks...
something like that. I need some advice, hints or  how to setup a
Xen+Heartbeat+some disk volume management configuration.
Thank you
Luke

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Luke,

You should be able to run drbd over lvm. Just give each vm it''s own
drbd
device, and it should work. This way you can failover each vm
individually.

Beware though that there is a bug in the interaction between Xen/LVM/DRBD,
but this can be worked around by specifying the disk image as tap:aio
instead of phy.

Niels
> Hello,
> I am trying to figure out the best way, how to configure a small cluster
> with xen and High Availability (Heartbeat). I have two servers and a few
> virtual machines. What I need is to ensure, that images or partitions of
> the machines will be mirrored between the two nodes (maybe with drbd?).
> But that is not all - I also need to enlarge the disks (because of
> growing databases) of virtual machines sometimes (if it could be done
> without shutting the machines down, it would be perfect!), so I am
> thinking about some evms/lvm setup. But I have no idea how to configure
> such a thing - how would it look like? Do you have any ideas, schematics
> or something? Like layered model - should I use evms to group drbd
> devices in domain 0 or lvm in virtual machines to group virtual disks...
> something like that. I need some advice, hints or  how to setup a
> Xen+Heartbeat+some disk volume management configuration.
> Thank you
> Luke
>
> _______________________________________________
> Xen-users mailing list
> Xen-users@lists.xensource.com
> http://lists.xensource.com/xen-users
>


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Niels,

Thanks for an advice, I will try it. But there is one thing I am
thinking about - how to manage the LVM2 PVs, VGs and LVs over the
cluster centrally? Next year I maybe get one more server and I will have
to add some new virtual machines and modify disk space given to the
existing ones. If I use just plain LVM2, I would have to configure it
node-by-node, step-by-step, manually, wouldn''t I? I found some HowTos
on
Novell pages, where they are using iSCSI and OCFS to manage storage for
virtual machines, but it doesn''t fit my needs. I don''t want to
setup
another machine to be an iSCSI target and so on. I am looking for a
simpler solution with DRBD  and Heartbeat,  which will also enable me to
manage the LVs for virtual machines centrally. I''ve found some
information that EVMS would maybe fit my needs, but it''s still new to
me
and I have no idea how to configure it to manage LVM2 partitions on
multiple machines or how it will interact with Heartbeat software. If
anyone knows about some configuration HowTos or something like that,
please, let me know.

Thanks,
Luke

P.S.
short overview of my current configuration:
2 nodes
both nodes running xen, Heartbeat, DRBD
mirroring of partitions (will try LVM2 LVs) via DRBD, if one node fails,
Heartbeat runs everything on the second

As I said, I am looking for a way how to better manage disk space and
easily add a new node/virtual machines.

> Luke,
>
> You should be able to run drbd over lvm. Just give each vm it''s
own drbd
> device, and it should work. This way you can failover each vm
> individually.
>
> Beware though that there is a bug in the interaction between Xen/LVM/DRBD,
> but this can be worked around by specifying the disk image as tap:aio
> instead of phy.
>
> Niels
>
>   

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