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Re: [Xen-users] Network Block Devices & Redundancy

To: Matthew Wild <M.Wild@xxxxxxxx>
Subject: Re: [Xen-users] Network Block Devices & Redundancy
From: Matthew Richardson <M.Richardson@xxxxxxxx>
Date: Fri, 07 Aug 2009 13:21:38 +0100
Cc: Xen User-List <xen-users@xxxxxxxxxxxxxxxxxxx>
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> Matthew,
>       wouldn't your RAID1 solution lead to more complex manual configuration
> for each domU? And you wouldn't have an easy route to domU migrations.
> If you use the DRBD+iSCSI route, you can connect to all your   targets
> on all your xen hosts, but only actually use the disk on the host with
> that domU on it. Live migration is then very easy.
> Cheers

Thanks for the comment.

In both cases you can have the iSCSI targets permanently connected to
all hosts (within reason, since I suspect there may be inefficiencies or
upper limits in doing this).

The only difference with the RAID1 approach is you need to start the
array on the new host before you do the migration, and stop it on the
old host.  This does mean that you have to take action on both old and
new hosts during migration, but this is easy enough to achieve =either
with simple scripts, or possibly with libvirt hooks.

This extra work might be a slight disadvantage, but when compared to the
removal of 'split brain' risks, I see if as being more than worth it.



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