[Linux-cluster] General question about cluster

[Robert Peterson]

Fedele Stabile wrote:
> Thank you for your suggestions.
> 
> I'm using CentOS 4.4 and the purpose of the cluster is sharing of user 
> filesystem.
> 
> I know that it's possible via NFS but i would experiment the cluster-suite.
> 
> If i don't user CS on student-PC can i use GFS instead NFS to export SAN 
> filesystems to student-PC?
> 
> Thank you
> Fedele STABILE

Hi Fedele,

One primary use of GFS is to allow cooperation of a "physically shared" 
file system between multiple nodes.  By physically shared, I mean
that the machines have access to the hardware, for example, through a
device driver.  That can be a SAN, iSCSI or whatever.  GFS does not 
export the storage to computers that don't have direct access.

It sounds like you have a SAN attached to your two servers, so
they should probably use GFS so they cooperate on the file system
properly.

It sounds like your student PCs are not connected to your SAN, so they
don't have direct access.  If you want them to have "network access" to
the SAN, you'll have to either use a network file system like NFS or
SAMBA to export the GFS file system from the servers to the PCs.
In this case, only the two servers need to be clustered.
 
Another (more complex) option is to export the block device associated 
with SAN on a server with GNBD (gnbd_export) and import the block device
to your student PCs with gnbd_import and mount the imported block
device as type GFS.  For example, on a server with the SAN, 
after cluster suite is started, do something like:

gnbd_serv
gnbd_export -d /dev/your_vg/your_lv -e san_storage
(where /dev/your_vg/your_lv) is the logical volume associated with
the SAN on your server.)

On your student PCs, do something like:

(Start the cluster sortware)
gnbd_import -i <server name>
mount -tgfs /dev/gnbd/san_storage /mnt/student

This way, all the student PCs are referencing the same storage
through the block device, but that means you would once again
have to put them all in the cluster so all their GFS file 
systems would cooperate on the file system.  And then you'd
have the same quorum problems when the student PCs are shut off.

I haven't used gnbd in a long time, so I'm a bit fuzzy about that
setup.

Regards,

Bob Peterson
Red Hat Cluster Suite