[Lustre-discuss] MD1000 woes and OSS migration suggestions

[Andreas Dilger]

On 2009-12-29, at 19:33, Nick Jennings wrote:
> Hi Everyone,

Hi Nick,

> We've been using an MD1000 as our storage array for close to a year
> now, just hooked up to one OSS (LVM+ldiskfs). I recently ordered 2  
> more
> servers, one to be hooked up to the MD1000 to help distribute the  
> load,
> the other to act as a lustre client (web node).
>
> The hosting company informs me that the MD1000 was never setup to
> operate in split mode (which I asked for in the beginning) so  
> basically
> only one server can be connected to it.
>
> I now am faced with a tough call, we can't bring the filesystem down
> for any extended period of time (a few minutes is OK, though 0  
> downtime
> would be perfect!) and I'm not sure how to proceed in a way that would
> make things cause the least amount of headache.
>
> The only thing I can think of is to set up a second MD1000 (configured
> for split mode) connect it to OSS2 (the new one which is not yet being
> used), add it to the Lustre filesystem and then somehow migrate the  
> data
> from OSS1 (old MD1000) to OSS2 (new MD1000) ... then, bring OSS1
> offline, and connect it to the second partition of new MD1000 and  
> bring
> that end online once more.

There is a section in the manual about "manual data migration", which  
should let you move the data.  Note that this is not 100% transparent  
to applications, but it is safe if you know either that files are  
unused, or only open for reading.

Cheers, Andreas
--
Andreas Dilger
Sr. Staff Engineer, Lustre Group
Sun Microsystems of Canada, Inc.