Node Pairing for Hot Online upgrade compatability.

[Richard Siemers]

We are about to undergo our first hot online inserv upgrade from 2.24 to 2.31 and have discovered some gotchas that were left out of the implementation guides that I thought I would share. This only applies to systems with 4 nodes or more.

In 4+ node systems, when have a need to zone a host to only 2 of the 4 nodes, which is our case as we have several servers with only a single HBA, you need to be aware that hot online upgrades will reboot HALF the nodes in a system at once... therefore, what they call "Vertical Pairing" should be avoided.

Since disk shelves are connected to a single node pair only, the law/rule becomes that only 1 node in a pair may go down or reboot at any given time (upgrade or not). So when picked which 2 nodes to use for a host in a 4+ node system, pick 2 horizontal nodes... such as 0 and 1, or 6 and 7... aka both halves of a node pair. As it stands presently, 3PAR will reboot all the evens or all the odds at once in a vertical stack, so if you're verticaly zoned, you will lose connectivity.

This is well documented in the 3PAR Upgrade Pre-Planning guide, however all implementation guides I have seen as of this date complete lack any mention of this issue or how to avoid it. Good thing the techs at 3Par perform a type of health check prior to the upgrade in order to identify and rectify such issues beforehand.