Re: [Xen-users] Advice on HighAvailable/Failover Xen machines

["Florian Heigl" <florian.heigl@xxxxxxxxx>]

Hi,

2007/11/28, Maximilian Wilhelm <max@xxxxxxxxxxx>:
> Hi!
>
> I want to accomplish the following setup:
>  Two (maybe leter more) Xen systems running on two machines with HBAs
>  inside connected to a SAN.
>
>  I would like to place the DomU block-devices on logical volumes on
>  top of a LUN of the SAN which is available at both (all) Dom0s.
>
> I read about the possibiliy to use EVMS as one solutions which could
> fullfil my needs.
>
> Is this a good idea?
> How could I do some kind of failover in case one Dom0 has gone?
> Can Xen detect this and move the affected DomUs automagically?
>
> Any hints how to set something like this up would be highly
> appreaciated.

I've played around a lot on this path.
With EMVS you can either use the cluster segment manager or the OCFS2 Plugin
with SAN Storage, either has it's advantages, both will nicely
integrate with Linux-HA / heartbeat.

EVMS also is greatly helpful for fully automated/scripted storage
setup etc which comes to mind for HA setups.

But, now for the downside:
EVMS is unfortunately quite dead, the OCFS2 plugin never made it into
mainline, the heartbeat integration needs patches, the BBR patches
need dm patches for the dom0 kernel, there is almost no irc support
left, the devs are.. well, i don't know where AND as it was designed
by IBM gurus it is really well thought through and perfectly
structured, but INCREDIBLY annoying to use!
Once you go into larger Xen setups you might have to handle 100s of
volumes and on occassion it might be manually - personally i think the
EVMS management is unbearable.

I still run my system on EVMS and i don't really see a good
alternative for a logical-volume based attempt (yes clvm exists but,
as always, can't mirror LVs in a feasible way)

for a new HA system i'd try to tie together opensharedroot(.org),
ocfs2 and the san, booting from ocfs2 root, with another volume(s) for
the domU images.
But that implies you don't use a JBOD on the san but higher end
(active-active) storage.

if your site has SDRF-ed EMC^2 Symmetrix that's no issue, otherwise it
might well turn into one.

Regards,
Florian


-- 
'Sie brauchen sich um Ihre Zukunft keine Gedanken zu machen'

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