Chris Samuel wrote: > 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 > tohave two options: You should be able to do this entirely within the dm-multipath layer. It can deal with multiple controllers as well as multiple fabrics. In dual controller/dual fabric setups, multipath should create four paths for each lun (2 fabrics * 2 controllers = 4 paths). However, not all dual controller arrays are active-active, some are active-passive. If the controller really is active-active, then the dm-multipath should round-robbin IO across all 4 paths (you can check that with iostat). (Example multipath output from an HP EVA8000) [size=3726 GB][features=1 queue_if_no_path][hwhandler=0] \_ round-robin 0 [prio=4][enabled] \_ 1:0:2:1 sdab 65:176 [active][ready] <--- Green Fabric, controller A \_ 0:0:2:1 sdaa 65:160 [active][ready] <----Red fabric, controller A \_ 0:0:3:1 sdac 65:192 [active][ready] <----Red fabric, controller B \_ 1:0:3:1 sdz 65:144 [active][ready] <----Green fabric, controller B If the controller is active-passive, then you will see 2 active paths, and 2 passive paths. (this example is from an HP EVA5000, where passive paths are labelled "ghost." The output may be different for other models of controller) [size=100 GB][features=1 queue_if_no_path][hwhandler=0] \_ round-robin 0 [prio=2][enabled] \_ 0:0:0:2 sdb 8:16 [active][ready] <---green fabric, controller A \_ 1:0:1:2 sdk 8:160 [active][ready] <---red fabric, controller A \_ round-robin 0 [prio=2][enabled] \_ 0:0:1:2 sde 8:64 [active][ghost] <---green fabric, controller B \_ 1:0:0:2 sdh 8:112 [active][ghost] <----red fabric, controller B If you are seeing something different, you need to mess with the path_grouping_policy and path_checker values in the multipath.conf file. The exact values depends on the exact model disk-controller you are using. I don't have any IBM storage, so can't help you with the exact values I'm afraid. The people on the dm-devel list should be able to help you with the actual values to use. http://sources.redhat.com/dm/ Cheers, Guy -- Dr. Guy Coates, Informatics System Group The Wellcome Trust Sanger Institute, Hinxton, Cambridge, CB10 1HH, UK Tel: +44 (0)1223 834244 x 6925 Fax: +44 (0)1223 496802 _______________________________________________ Beowulf mailing list, Beowulf@beowulf.org To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
