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
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