Cott Lang wrote: > 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? :) 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 _______________________________________________ linux-lvm mailing list linux-lvm@redhat.com https://www.redhat.com/mailman/listinfo/linux-lvm read the LVM HOW-TO at http://tldp.org/HOWTO/LVM-HOWTO/
