On Tuesday, 02/17/2015 at 07:10 EST, Berthold Gunreben <b...@suse.de> wrote: > There are some advantages to KVM on System z too: > - Network bond balance-rr to have shared network devices and high > availability network (active-passive does not count as highly > available network for certain external switches).
(cough) Why would you classify balance-rr as an 'advantage', Berthold? That's a primitive per-packet (subject to packets_per_slave) round robin distribution. a truly horrible idea since in an HA environment those two adapters go to different switches. All you're doing is increasing the risk of out-of-order packet arrival at the destination, burning CPU time to reassemble the TCP segments and delays segment delivery to the socket (app). At least use balance-xor so that the assignment to an adapter is made based on MAC address and is persistent unless there's a failure. Add xmit_hash_policy layer3+4 and you have winner. (You really want layer3+4, but you can't use it with balance-rr.) But these days there's really no excuse for not using IEEE 802.3ad. It's standard on a switch of any reasonable vintage, and these days they all include support for multi-switch port groups (aka "virtual chassis"). MVS has per-packet load balancing, too. It was abandoned in favor of per-TCP session distribution (layer3+4). Since data queued on a virtual NIC is immediately copied into CP and the guest QDIO queues cleared, multiple NICs to the same VSWITCH (and VLAN) serve only to spend more CPU time getting the data to the same place (an outbound OSA queue). IEEE 802.3ad takes are of distributing that traffic among the OSAs in the port group. And one related cautionary note: I recently learned that you shouldn't put unbonded adapters on the same subnet without doing your homework. By default, Linux will consolidate all traffic onto just one of those adapters, it having all of the same-subnet IP addresses consolidated onto it. (Very odd when you see QUERY VSWITCH DETAILS output showing adapters with no IP addresses and others with more than one!) I'm not really sure *why* Linux does that, but I'm guessing that it's an x86 thing. Or, it could just be to annoy me. Alan Altmark Senior Managing z/VM and Linux Consultant Lab Services System z Delivery Practice IBM Systems & Technology Group ibm.com/systems/services/labservices office: 607.429.3323 mobile; 607.321.7556 alan_altm...@us.ibm.com IBM Endicott ---------------------------------------------------------------------- For LINUX-390 subscribe / signoff / archive access instructions, send email to lists...@vm.marist.edu with the message: INFO LINUX-390 or visit http://www.marist.edu/htbin/wlvindex?LINUX-390 ---------------------------------------------------------------------- For more information on Linux on System z, visit http://wiki.linuxvm.org/
