[lustre-discuss] Lustre snapshots

[Andreas Dilger]

Yes, from the Lustre point of view, the snapshots are currently totally separate filesystems.

You would need to generate the automount map from "lctl snapshot_list".  However, if you mounted a client on the MGS temporarily after creating the snapshot you could write the automount map into e.g. "/mnt/lustre/.snapshot/automountmap" so that it would immediately be visible to all clients mounting the filesystem, and immediately unmount the filesystem again.  Of course you could use some other mechanism to distribute it as well.

Cheers, Andreas

On May 30, 2019, at 08:26, Hans Henrik Happe <happe at nbi.dk> wrote:
> 
> 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
> Snapshot).
> 
> 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.
> 
> Cheers,
> 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
>> 

Cheers, Andreas
--
Andreas Dilger
Principal Lustre Architect
Whamcloud