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

Michael O'Sullivan michael.osullivan at auckland.ac.nz
Thu May 22 02:12:27 UTC 2008

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.

Thanks, Mike

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