[Linux-cluster] GFS, iSCSI, multipaths and RAID

[Wendy Cheng]

Michael O'Sullivan wrote:
> Hi Alex,
>
> We wanted an iSCSI SAN that has highly available data, hence the need 
> for 2 (or more storage devices) and a reliable storage network 
> (omitted from the diagram). Many of the articles I have read for iSCSI 
> don't address multipathing to the iSCSI devices, in our configuration 
> iSCSI Disk 1 presented as /dev/sdc and /dev/sdd on each server (and 
> iSCSI Disk 2 presented as /dev/sde and /dev/sdf), but it wan't clear 
> how to let the servers know that the two iSCSI portals attached to the 
> same target - thus I used mdadm. Also, I wanted to raid the iSCSI 
> disks to make sure the data stays highly available - thus the second 
> use of mdadm. Now we had a single iSCSI raid array spread over 2 (or 
> more) devices which provides the iSCSI SAN. However, I wanted to make 
> sure the servers did not try to access the same data simultaneously, 
> so I used GFS to ensure correct use of the iSCSI SAN. If I understand 
> correctly it seems like the multipathing and raiding may be possible 
> in Red Hat Cluster Suite GFS without using iSCSI? Or to use iSCSI with 
> some other software to ensure proper locking happens for the iSCSI 
> raid array? I am reading the link you suggested to see what other 
> people have done, but as always any suggestions, etc are more than 
> welcome.
>

Check out dm-multipath (*not* md-multi-path) to see whether you can make 
use of it:
http://www.redhat.com/docs/manuals/csgfs/browse/4.6/DM_Multipath/MPIO_description.html

-- Wendy