The IBM z/VM Operating System <[email protected]> wrote on 12/10/2007 08:33:38 AM:
> Ray, > You mention number of usable NPIV subchannels are subject to the > switch limitations. > > Are switch limitations what the IBM Redbook is referencing when it > says don't "use more than 32 subchannels per physical channel in NPIV mode"? > With the Brocade switch I could use 255 subchannels in NPIV mode? > > (see "Introducing N_Port Identifier Virtualization > for IBM System z9" page 4 > http://www.redbooks.ibm.com/redpapers/pdfs/redp4125.pdf ) > > " Configuration considerations > Some general recommendations for using NPIV include: > Do not use more than 32 subchannels per physical channel in NPIV mode. > Also, do not perform more than 128 total target logins (for > example, in a configuration with 32 subchannels, limit the number of > target logins to no more than an average of 4). Using more > subchannels, target logins, or both can create timeouts." > > John, Yes, this is partially a switch limitation. The process to log an NPIV port into the fabric takes milliseconds. When there are lots of these, the time becomes seconds. When we did NPIV bringup, we discovered situations where linux would time out and escalate its recovery. The easiest way to cause this is with fibre pulls. Though, any event that causes link down, up should lead to it too. FWIW, using lots of small zones may help alleviate these operating system time outs. When the link goes down/up, the number of state change notifications generated by the the switch will be less. So the switch will have more resources to handle logins. If you are brave, you can try to use more NPIV subchannels. There is nothing in the FCP firmware to prevent you from doing so. Keep in mind that when we make configuration recommendations, we have to make them for the worst case. It's nice to hear that people are actually interested :) Ray Higgs System z FCP Development Bld. 706, B24 2455 South Road Poughkeepsie, NY 12601 (845) 435-8666, T/L 295-8666 [EMAIL PROTECTED]
