[lustre-discuss] Lustre snapshots

Hans Henrik Happe happe at nbi.dk
Thu May 30 07:26:46 PDT 2019

It's only the mapping from the snapshot name to hex value used for
mounting I'm asking about. It's explained in the doc (30.3.3. Mounting a

The client cannot call 'lctl snapshot_list'. Guess the main fs and its
snapshot fs' are so separated that putting the mappings in the client
/proc structures of the main fs would become ugly.

We will just communicate client mount name through another channel.

Hans Henrik

On 30/05/2019 10.05, Andreas Dilger wrote:
> On May 30, 2019, at 01:50, Hans Henrik Happe <happe at nbi.dk> wrote:
>> Hi,
>> I've tested snapshots and they work as expected.
>> However, I'm wondering how the clients should mount without knowing the
>> mount names of snapshots. As I see it there are two possibilities:
>> 1. Clients get ssh (limited) access to MGS (Don't want that).
>> 2. The names are communicated through another channel. Perhaps, written
>> to a file on the head Lustre filesystem or just directly to all clients
>> that need snapshot mounting through ssh.
>> If there isn't a better way, I think number two is the way to go.
> You could use automount to mount the snapshots on the clients, when they are needed.  The automount map could be created automatically from the snapshot list.
> Probably it makes the most sense to limit snapshot access to a subset of nodes, such as user login nodes, so that users do not try to compute from the snapshot filesystems directly.
>> Guess the limited length of Lustre fs names is preventing the use of the
>> snapshots names directly?
> If you rotate the snapshots like Apple Time Machine, you could use generic snapshot names like "last_month", "last_week", "yesterday", "6h_ago" and such and not have to update the automount map.  The filesystem names could be mostly irrelevant if the snapshot mountpoints are chosen properly, like "$MOUNT/.snapshot/last_month/" or similar.
> Cheers, Andreas
> --
> Andreas Dilger
> Principal Lustre Architect
> Whamcloud

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