[Linux-cluster] optimising DLM speed?

Alan Brown ajb2 at mssl.ucl.ac.uk
Thu Feb 24 18:37:24 UTC 2011

Steven Whitehouse wrote:

> As soon as you mix creation/deletion on one node with accesses (of
> whatever kind) from other nodes, you run this risk. 

_ALL_ the GFS2 filesystems (bar one 5Gb one for common config files, 
etc) are mounted one-node-only.

_ALL_ the GFS2 filesystems (with the same exception) are NFS exported.

NONE of the NFS exported filesystems have local processes accessing them 
except for backups(*) - because there's distinct and non-theoretrical 
risk of file coruption if anything other than NFSd touches a 
NFS-exported filesystem (We've experienced it and I've reproduced the 
corruption on non-cluster systems).

Even Samba is a re-export from a NFS client and I've been toying with 
the idea of moving backups to a NFS client despite the network penalties.

(*) Backups run on the node where the filesystem is NFS exported.

> Obviously you wouldn't be using a cluster filesystem if you didn't intend to have this
> kind of access from time to time, but anything that can be done at the
> application level to help improve locality will pay big dividends
> compared with any tuning that can be done at the fs/dlm level.

We originally installed this to run as pNFS/SAMBA/iscsi fileservers but 
after encountering the NFS corruption issues and finding out just how 
much slower it gets if other nodes mount/access the filesystems we just 
use GFS to ensure corruption-free failover.

Let's just say that what was promised was not what was delivered...

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