[Gluster-devel] Re; Xen on Gluster

Gareth Bult gareth at encryptec.net
Mon Feb 4 11:53:04 UTC 2008


(this applies to Xen 3.1 and 3.2 with Gluster TLA) 

I don't know if anyone can clarify this for me, if not I know a number of people 
are trying the same thing as we are, so just a summary of what I've found; 

Xen works on Gluster using the FILE: driver. (and works fine) 
Xen does not seem to work using the AIO driver. 
Redhat people tell me I shouldn't be using FILE: as it's very dangerous .. so I got a little 'stuck'. 

Can someone confirm that AIO is the preference and any ideas why it might not work on Gluster? 
(warning: attempting to use AIO on a GlusterFS can render the machine unusable without a reboot) 

Is anyone at Gluster looking at Xen on Gluster, if so, are you aware of this issue? 


FILE: does not work properly with gluster in the context of attaching and detaching block devices. 
(I've no idea why .. or even if AIO "does" work .. ) 

I've just switched to OCFS2 .. which DOES work with AIO, so this "appears" to be a Gluster problem. 

For Ubuntu people: 

The Xen kernel on Gutsy is broken, expect to have problems if you stress it. 
My solution was to switch to a RH 2.6.21 kernel which "seems" to be fine and does not display the same faults as the Ubuntu 2.6.2x kernel. 
(If you switch to the raw 2.6.18 kernel as supplied by Xen, you are likely to break Gluster, 2.6.21 works Ok) 

For what it's worth I was dreading having to get DRBD working with OCFS2 ... as it turns out it was fairly painless and it seems pretty stable ... unless of course you have a mix of kernels .. 2.6.21 OCFS for example won't talk to 2.6.24 kernels .. :( [protocol v7 -> protocol v8] 


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