Re: [Xen-users] cluster filesystems

[Mark Petersen <mtp@xxxxxxxxxx>]

At 11:35 AM 4/11/2006, you wrote:
> The best idea i have come up (though i wont be able to try it for 
> some time) with with minimal patching is this:
> Use ocfs2 as file system,
> Use nbd+md to make a "networked raid"
> use iSCSI to export this network raid to Xen parent hosts,
> My question to those of you with better know how:
>    Will this allow live migration (assume yes as now because of the 
> "real" block device shown by ocfs2)
>    Will domU's living on the file system survive a file system node 
> failure? (this is the who point of this thread)
> Brock
How exactly will nbd+md failover?  Does ocfs2 actually export "real" 
block devices, or are you just going to store disk images in a file 
on ocfs2?  I thought ocfs2 was a filesystem.  I don't know enough 
about ocfs2 to answer your second question, but I think the answer 
lies in how nbd+md will failover and offer the ocfs2 
filesystem.  Obviously there's some potential for data loss on the nbd.
This sounds similar to what I've been trying to accomplish with drbd 
and gnbd.  You can run drbd/gnbd without any patching, you just have 
to build modules against your kernel source, and then install the 
various packages to manage them.  Depending on your time frame, 
drbd0.8 will make active/active configurations possible and you could 
run gnbd multipath, this would be a truly redundant setup with no 
failover trickery necessary.  There is a relatively new pre-release 
of drbd0.8, but I'm not sure what the actual release time frame is.
I'm also considering iscsi-target with drbd but it doesn't currently 
offer multipath, so I'm not sure how cleanly it could failover.

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