[Beowulf] OT: Software RAID & Multipath

Chris Samuel csamuel at vpac.org
Mon Jan 8 15:01:35 PST 2007

This is about a storage node for a cluster, so it's partly on topic.. :-)

Through happy coincidence we now have a box with two FC cards going to a SAN 
switch and thence into each side of an IBM FAStT 600 (doing H/W RAID5).  The 
FAStT is partitioned into two 1.6TB lumps and each FC card can see both 
controllers on the FAStT (for failover).

Booting a live CD shows me that the multipath-tools package automatically 
detects it has two paths and sets this up appropriately (very nice).

Now, if I wanted to stripe accesses to the FAStT down each controller I seem 
to have two options:

1) Use software RAID-0 with MD.  My concern then is that I don't know whether 
the RAID-0 will kick in *before* the multipath and think it can stripe over 4 
drives (which would be bad).

2) Add both multipath'd partitions as PV's to LVM2 and then every time we 
create a new logical volume we MUST remember to specify the stripe option for 
lvcreate for it to work.  I also don't know how efficient or reliable it is..

Thoughts anyone ?

 Christopher Samuel - (03)9925 4751 - VPAC Deputy Systems Manager
 Victorian Partnership for Advanced Computing http://www.vpac.org/
 Bldg 91, 110 Victoria Street, Carlton South, VIC 3053, Australia

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