On Wed, Nov 4, 2009 at 4:36 PM, Nils Goroll <slink at schokola.de> wrote:
> Hi Buni and Hartmut,
>
> thank you both for your explanations.
>
> Binu, the explanation you gave regarding PxFS is along the lines of what I'd
> expected.
>
> Can we summarize the topic like this?
>
> * To make fssnap work on PxFS ("global") mounts, several additional
> requirements regarding the PxFS layer and PxFS/UFS interoperation had to be
> fulfilled, so it seems to be far from trivial to implement fssnap on PxFS.
>
> * For non-PxFS ("HA-local") mounts, fssnap should work technically, even
> though it is not supported. Care should be taken to minimize the impact of
> the necessary I/O pauses during the snapshot process, for instance by
> temporarily disabling cluster monitoring of resources depended upon the
> filesystem to be snapshotted.Even for non-HA mounts, the project complexity will be the same. The difference between HA and non-HA PxFS is in the server/master where the underlying UFS will be wrapped in a failover capable object or not. All client/server communication is identical. In both cases all fs activity should be stopped by the server while the snapshot is in progress. If snapshotting is supported in some manner, the difference for non-HA PxFS server will be to not check whether a snapshot is in progress before allowing a switchover. Please keep in mind that I am not speaking from a proven as implementable idea, just guessing at what is possible. cheers Binu > I'll see where I get from here. > > Hartmut, regarding your comment: > >> The problem is with the data and state of fssnap if a node should die >> during fssnap taking the snapshot. > > Sure, UFS snapshots are temporary (see fssnap_ufs(1M)), but IIUC, > snapshotting an ha-local FS in a cluster should not be any different from > snapshotting any other (non-root) FS in that the (clustered or non > clustered) node may die at any time, so the snapshot will get lost, right? > > Again, thank you very much! > > Nils > >
