[Lustre-discuss] Moving storage from one OSS to another

[Kevin Van Maren]

Rafa Griman wrote:
> Hi all :)
>
> Got a customer

(It is quite bad form to ask for help for a commercial deal without 
using your work email address.  I assume you still work for Bull?)

> with:
>      - 1 x S2A9900 (one couplet)
>      - 500 x 2 TB drives
>      - 4 OSS
>
> This customer wants to add:
>      - 1 x S2A9900 (one couplet)
>      - 300 x 2 TB drives
>      - 4 OSS
>
> I know we could "just add" and restripe the existing files. But the
> customer wants to physically move 100 drives from the existing S2A9900
> to the new one in order to have 400 drives on one S2A9900 and 400
> drives on the other one.
>
> So my questions are:
>      1.- Can this be done (move drives between OSTs) without losing data?
>   

First, make sure DDN supports moving drives _data intact_.  The drives 
in each tier will at least have to end up as an ordered tier for this to 
work, but I would guess it isn't quite so simple.

>      2.- Can an OST be moved from one OSS to another without losing data?
>   

Yes, IF it is done properly.

Step 1, back up all essential data.

Step 2, add the _new server_ as a failover node for the OSTs being 
moved.  Note that this requires a "tunefs.lustre --writeconf" (with new 
parameters on the OSTs being moved) and re-mounting all the servers.

Step 3, move the drives

Step 4, update the server/failover NIDs, removing the old ones with 
another writeconf pass.


I _strongly_ recommend that you verify their Lustre support contract is 
current, and that you do a dry-run in a test environment before doing it 
live (if nothing else, you do have 4 servers and a new couplet to play 
with).

>      3.- Has anyone done this? How?
>
> I imagine it can be done restriping files/migrating files within the
> Lustre filesystem, removing "empty" OSTs, ...
>   

Well, yes, there is that option as well; use lfs_migrate (at least 2 
passes).

> TIA
>
>    Rafa
>   

Kevin