PowerCLI: Balance LUN paths for a Cluster

As I’ve been managing more and more infrastructures using fibre channel storage, I’ve found that it’s been somewhat difficult to keep the LUN paths to each host balanced. By balanced, I mean that for each LUN to each host, there is a number of paths and I want to make sure that, for example, each LUN 10 to each of the hosts is using path A as the primary and path B as the stand by. LUN 11 uses path B as the primary, LUN 12 back to path A, and so on.

It so happens that I’m using a DMX-4 for storage, and the policy we have is to use a fixed path policy. I realize that Round Robin would make this entire script moot, well, except for making sure that the PSP is correct. I also realize that PowerPath would be the ideal solution for EMC storage, but we don’t use it…that’s a story for another day.

This script is, admittedly, long…longer than I expected it to be. The original inspiration for this script came from Justin Emerson’s very functional and succinct script, however I was not satisfied with the way LUNs were balanced. His script queries the host for LUNs then sorts them by canonical name and round robins the paths based on the number of paths present for the first LUN.

This works well, so long as all the LUNs are present on all the hosts and they all have the same number of paths. I can only presume that he assumes that those cases have already been checked for, and fixed, prior to execution. I wanted to do that all in one script.

Additionally, and it’s rather petty, I wanted the LUNs to be balanced based off their LUN identifier rather than the canonical name…they don’t always follow the same order, and in the case of my hosts with two HBAs (and consequentially, two paths per LUN), I wanted all odd LUNs to use one path for the primary and all even LUNs to use the other. Justin’s script does an excellent job of ensuring that the paths are evenly distributed, as you will end up with the same number on each, but not in the pretty fashion I desired.

Also, thank you to Glenn, who helped me “powershellize” this script…my PowerShell looks and reads like Perl, and therefore doesn’t use a lot of the optimizations that PoSH brings…such as automatic parameter handling and other niceties.

So, without further ado…

1 thought on “PowerCLI: Balance LUN paths for a Cluster”

  1. Hi,
    I’m not sure that only Active paths are used with this script. With ALUA (and so Fixed_AP), usualy half paths are optimal ones. So it would be good if only these optimal paths was part of the round robin distribution.

    I think this modification should be done :
    $paths = Get-ScsiLunPath -ScsiLun $lun | where-object {$_.State -eq ‘Active’} | Sort-Object -Property SanID

    I’ll try this.
    Cedric.

    Reply

Leave a Reply