Re: [Xen-users] iscsi vs nfs for xen VMs

[Javier Guerra Giraldez <javier@xxxxxxxxxxx>]

2011/1/28 Christian Zoffoli <czoffoli@xxxxxxxxxxx>:
> Il 28/01/2011 08:08, yue ha scritto:
>> what is the performance of clvm+ocfs2?
>> stability,?
>
> it's very reliable but not as fast as using clvm directly.

to expand a little:

ocfs2:
it's a cluster filesystem, it has the overheads of being a filesystem
(as opposed to 'naked' block devices), and of the clustering
requirements: in effect, having to check shared locks at critical
instants.

clvm:
it's the clustering version of LVM.  since the whole LVM metadata is
quite small, it's shared entirely, so all accesses are exactly the
same on CLVM as on LVM.

the only impact is when modifying the LVM metadata
(creating/modifying/deleting/migrating/etc volumes), since _all_
access is suspended until every node has the a local copy of the new
LVM metadata.

Of course, a pause of a few tens or hundreds of milliseconds for an
operation done less than once a day (less than once a month in many
cases) is totally imperceptible.

-- 
Javier

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