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Re: [Xen-users] cluster filesystems

  • To: xen-users@xxxxxxxxxxxxxxxxxxx
  • From: Brock Edward Palen <brockp@xxxxxxxxx>
  • Date: Tue, 11 Apr 2006 17:07:00 -0400
  • Delivery-date: Tue, 11 Apr 2006 14:09:18 -0700
  • List-id: Xen user discussion <xen-users.lists.xensource.com>

Mark Petersen wrote:
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)

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.
Yeah ocfs2 is a file system, I realized the miss wording after i replied my apologies. Im thinking yes they would have to be files, which isnt ideal, but again im looking for migration with survivability in a block device (host) failing.
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.
all i can say is awesome, ive looked into drbd before i was using xen, it looked like dev was very slow beyond making it work. active active drbd would still require a cluster file system such as ocfs2 to keep things from tromping on each other. Thankyou for the heads up.

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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