[lustre-discuss] Adding a servicenode (failnode) to existing OSTs

[Steve Barnet]

Hi all,

   We have a multipath OSS->OST hardware configuration which,
in principle, allows us to move OSTs between OSSes if/when
we need to do maintenance. In general, this has worked very
well for us.

   However, today when I needed to do some maintenance, I
discovered that we have a set of OSTs that were not formatted
for failover (no service nodes specified at creation time).

So after a bit of noodling around, it looks like we should be
able to add these after the fact. Groovy! There appear to be a
couple ways that this could be done:

a) Add the service nodes:
    tunefs.lustre --servicenode=nid,nid /dev/<OST>

b) Add a failover node:
    tunefs.lustre --param="failover.node=<nid> /dev/<OST>


So a few questions:

1) Is one form preferred over the other? It seems like just
    specifying service nodes might be better than being
    specific about primary vs. failover.

2) Will this be visible to the clients right away, or will
    additional steps be needed? I could see needing to remount
    the filesystem on the clients, or writeconf or something similar.

3) Any other gotchas I should be wary of?

Thanks much!

Best,

---Steve