[Lustre-discuss] Dedicated MGS?

[Andreas Dilger]

On Nov 18, 2007  20:48 -0500, Charles Taylor wrote:
> If a site has multiple Lustre file systems, the documentation implies  
> that there only needs to be a single MGS for an entire site  
> (regardless of the number of file systems).     However, I also know  
> it is fairly common to have a combined MGS/MDT.     So here are the  
> questions.
> 
> 1. If we are going to have several Lustre file systems, is there any  
> reason not to create each one with its own combined MGS/MDT?

Not that I'm aware of, with the restriction that you can only have a
single MGS running on a node at a time.  If you have failover MDSes,
then they need to share an MGS.

> 2. Can an MGS which is a combined MGS/MDT for one file system serve  
> as the MGS for one or more other file systems where the MGS and MDT  
> are separate?

It's possible, but seems klunky...  It means the combined MGS/MDT needs
to be started to also start the other filesystems.

> 3. Is there any reason why doing several separate combined MGS/MDTs  
> (one for each file system) won't work?

See above.

> What are other sites w/ multiple Lustre file systems doing?    A  
> dedicated MGS seems like a costly option.

A dedicated MGS doesn't mean a wholly separate node.  It might just
be a small partition shared among a few failover nodes.

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