[Lustre-discuss] How to start

[Daire Byrne]

Rayentray,

----- "Rayentray Tappa" <rtappa.ascentio at gmail.com> wrote:

> I'm testing this in order to build a large system later, where high
> availability of the data store is a must - so we do want to check how
> this works, what involves to configure it and what may happen in case
> of failure and how to restore it. 
> 
> If it can be configured in a later stage, i.e. after having already
> tested Lustre itself, it might be a good idea to learn only a few
> things at the time :)

Fair enough. I would think you can add failover at a later stage using
"tune2fs.lustre" but one of the developers/gurus will need to verify that.

> Our idea is to have a main Lustre running, which will be replicated
> in other two buildings. We still don't know how we will handle the
> replication, maybe Lustre1.8 is already out then and we can use that,
> or maybe we handle it with a separate unit of software that we need to
> develop anyway with other purposes[1]. Does it make sense to have
> only one MGS in that configuration?

If your network between the buildings is pretty solid then a single MGS
should be fine - it doesn't really do very much I/O. We have 4 buildings 
and a single MGS (with consistently low loads).

There is some work going on to write replication tools atm called 
"lreplicate". You can watch the progress here:

  https://bugzilla.lustre.org/show_bug.cgi?id=16855

However this is geared towards using "changelogs" which I don't think
are due until Lustre v2.0 which may be a way off yet. Again the devs
can better clarify that for you.

> [1] How easy/difficult is to become involved with Lustre development?
> I want to propose to the organization that, given we need replication
> and Lustre intends to provide it in version 2.0, we may help with its
> development. How much work would that be? (rough idea). Anyone I can
> contact specifically about this?

We do backups from a few Lustre filesystems to a large single Lustre 
filesystem using "e2scan" which can quickly scan the MDT for changed 
files and dump out a list which can then be fed into something like 
rsync and rm to synchronise filesystems. The Lustre e2fsprogs RPM includes
e2scan. I'm more than happy to send our bash script but it is pretty 
hack-tastic!

Daire