Re: [Xen-users] Re: cLVM on Debian/Lenny

[Javier Guerra <javier@xxxxxxxxxxx>]

Jan Kalcic wrote:> Now I think I can figure out that there is no difference 
between a domU
> based on a file block device on top of a cluster file system, let's
> suppose OCFS2, and a domU based on physical block device on top of LVM
> (cLVM). In both case, I am eventually able to run the domU on both nodes
> having data corruption. Neither OCFS2 nor cLVM with their different lock
> managers can provide that mechanism to assure consistency. Right? If
> yes, I would say that the best solution should always be using LVM, at
> least it provides more features.

right.  they manage very different things (cLVM gives you blockdevices, while 
OCFS gives you files); but Xen can use either one for the same purpose (storage 
for DomUs), and neither of them will prevent several nodes clashing each other 
when using the same 'thing' (file or blockdevice) at the same time.  just like 
a non-cluster filesystem can't prevent two different processes from corrupting 
a datafile by writing at the same time.

for that there are some scripts for HA (hearbeat2) that manage Xen instances as 
'cluster resources', and make sure that each one is running on exactly one node.


-- 
Javier

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