[DRBD-user] Is VMFS5 "cluster aware"?

Pascal BERTON pascal.berton3 at free.fr
Wed Nov 30 16:18:53 CET 2011

Note: "permalinks" may not be as permanent as we would like,
direct links of old sources may well be a few messages off.

Hi Dan!

VMFS is a clustered filesystem by nature, in the sense it allows concurrent
read-write accesses from up to 32 nodes simultaneously, it's not
specifically as of version 5.
Unfortunately you (still) have no mean to replicate it safely in
dual-primary mode with DRBD like you would do with OCFS2 or alike because
the lock management is achieved differently. This doesn't change in v5.
The main features that prevent the use of dual primaries are VM snapshots
and Thin provisioning, that induce regular block allocations. If you don't
use these features, you probably could use it fairly safely...

Thin provisioning is not the default option when creating a vDisk, therefore
you should be basically safe against that.

Snapshot is another story : To prevent snapshots, you will have to create
your vDisks in independent-persistent mode, which is not the default mode.
If you fail to do so, there's no mean to prevent the VM from doing a
snapshot, this regular block allocation will occur, and you take the risk of
data corruption.

Also, if you were to create 2 VMs exactly simultaneously, one on both ends
of the storage chain, there's a risk that both VMs point to the same
mirrored area, again leading to corruption... This case has but a few chance
to happen, but there's no way to prevent it to occur, and thus it's a risk!

Same story with Storage Vmotion, if 2 simultaneous operations were to be
launched at the very same time on both ends, you take a risk. Again,
probably rare, but no way to protect against it.

And there might be other cases where this could happen that I don't
immediately remind of...

So in any case, and especially for production, you'd better forget it and
keep your single-primary approach, if latency is effectively a cost,
corruption is an even worse one! :)

Best regards,


-----Message d'origine-----
De : drbd-user-bounces at lists.linbit.com
[mailto:drbd-user-bounces at lists.linbit.com] De la part de Dan Barker
Envoyé : mercredi 30 novembre 2011 14:20
À : drbd List
Objet : [DRBD-user] Is VMFS5 "cluster aware"?

Is the new filesystem for VMWare's vSphere 5 cluster aware? I continue to
see references to GFS2 and OCFS2 but never a mention of VMFS5. I'm just
curious for now, because I'm running single primary. If I could save the
network latency for reads from one host that would be sweet!


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