SAN Storage/mirror/lvm
Quoted 9 lines
I setup a similar system on a HDS-9570 but with only one card in each machine - 'assuming' that the failover in the driver would cope if a controller on the HDS failed (as opposed to a QLogic failure)
This worked fine if I disconncected a path in the fabric but when we took a controller of line the failover failed.
Since then I have used md multipath which has tested fine
I have a similar issue, two storage processors, two HBAs, and redundant paths between them.
On the host, I see 4 SCSI devices, two valid, two invalid - I'm guessing this is caused because only one storage processor exports a particular LUN, so half the paths are invalid until a storage processor fails over.
sdd - SP A Path 1
sde - SP B Path 1
sdf - SP A Path 2
sdg - SP B Path 2
I have a LUN currently on SP B, so I can use md multipath configured with /dev/sde and /dev/sdg, and that seems to work.
However, two things:
1) How do I set this up to handle a failover to SP A?
2) Multipath only seems to work in failover mode, is there a way to load balance across the two paths?
Anyone have any hints? :)
Quoted 13 lines · Cott Lang
On the host, I see 4 SCSI devices, two valid, two invalid - I'm guessing this is caused because only one storage processor exports a particular LUN, so half the paths are invalid until a storage processor fails over.
sdd - SP A Path 1
sde - SP B Path 1
sdf - SP A Path 2
sdg - SP B Path 2I have a LUN currently on SP B, so I can use md multipath configured with
/dev/sdeand/dev/sdg, and that seems to work.
Quoted 7 lines
However, two things:
1) How do I set this up to handle a failover to SP A?
2) Multipath only seems to work in failover mode, is there a way to load balance across the two paths?Anyone have any hints? :)
Hello Cott,
your questions and the phenomena you see are likely to be specific to your hardware. I tried Emulex and QLogic HBA and found very different behaviour.
Multipathing is handled by the storage systems differently from dumb disks. Load balancing over several physical paths is therefore a complicated task. Most vendors do not really support it. Some systems suffer from a Host switching paths. Unless you do not use a supported (read: expensive) Software you should keep your hands off.
Even failover has a 'mechanical' quality: you can hear the door's angles squiek when it happens.
I found my clusters diving after teardown of a storage's HBA.
Failover while switching the physical path, i.e. switching the HBA takes at least 45 second on a (tuned) qlogic. Meanwhile the whole computer freezes. The driver seems to switch off interrupts or something.
Have fun finding your solution.
Thomas