May 17

Print this Post

Why is my pathing policy limited to “fixed” or “MRU” with things like MSCS cluster?

Yesterday I received an email from someone. He wanted to know why he was limited to using either the “fixed” or “MRU” pathing policy for the LUNs attached to his MSCS cluster. In his environment they used round-robin for everything and not being able to configure all of them with the same policy was against their internal policy. The thing is that if round-robin would be used and the path would switch (by default every 1000 I/Os) the SCSI-2 reservation would need to be re-acquired on this LUN. (MSCS uses SCSI-2 reservations for their cluster devices) As you can imagine that could cause a lot of stress on your array and could lead to all sorts of problems. So please do not ignore this recommendation! Some extra details can be found in the following KB articles:

Why is my pathing policy limited to “fixed” or “MRU” with things like MSCS cluster?” originally appeared on Yellow-Bricks.com. Follow us on Twitter and Facebook.
Available now: vSphere 5 Clustering Deepdive. (paper | e-book)

Permanent link to this article: http://www.startswithv.com/2012/05/17/why-is-my-pathing-policy-limited-to-fixed-or-mru-with-things-like-mscs-cluster/