Re: [Xen-users] cluster filesystems

[Brock Edward Palen <brockp@xxxxxxxxx>]

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)
> > 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.
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.
Brock
> 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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