| |
|
 |
|
 |
|
|
|
| |
|
|
xen-users
RE: [Xen-users] iscsi vs nfs for xen VMs
>
> 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.
Microsoft achieve high performance with their cluster filesystem. In fact the
docs clearly state it's only reliable for Hyper-V virtual disks, any other use
could cause problems, so I assume they get around the metadata locking problem
by isolating each disk file so there are no (or minimal) shared resources.
>
> 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.
>
The dealbreaker for me with clvm was that snapshots aren't supported. I assume
this hasn't changed and even if it has, every write to a snapshotted volume
potentially involves a metadata lock so the performace drops right down unless
you can optimise for that 'original + snapshot only accessed on the same node'
case, which may be a limitation I could tolerate.
James
_______________________________________________
Xen-users mailing list
Xen-users@xxxxxxxxxxxxxxxxxxx
http://lists.xensource.com/xen-users
|
|
|
| |
|
Home