thinking sysadmin

I’ve written about running VMware ESX with VM swap on an NFS datastore previously – specifically whether or not it was supported/recommended:

• ESX Swap on NFS or Not?
• VMware about ESX swap on NFS: It’s okay

After writing the second post, I thought the issue was pretty much resolved: From multiple sources, the consensus seemed to be that running ESX with VM swap on NFS would be fine.  Imagine my surprise (and disappointment) at seeing the following VMware KB article 1008091, updated yesterday: An ESX virtual machine on NFS fails with swap errors. Further details are in the article itself, but VMware’s KB site is throwing intermittent errors for me at the moment, so I’ll provide the money quote:

The reliability of the virtual machine can be improved by relocating the swap file location to a non-NFS datastore. Either SAN or local storage datastores improve virtual machine stability.

In case you’re curious/adventurous/broke enough to try configuring your VMotion network on Fast Ethernet instead of Gigabit Ethernet, here’s what you can expect.

First, a warning from your VI client that you’re venturing into unsupported territory:

A friendly warning

And then, if you go ahead with the VMotion, a slight pause on the VM in question.  The following is output from running while true; do date; sleep 1; done on a Linux guest during the VMotion:

Tue Feb  3 13:23:17 PST 2009
Tue Feb  3 13:23:18 PST 2009
Tue Feb  3 13:23:19 PST 2009
Tue Feb  3 13:23:20 PST 2009
Tue Feb  3 13:23:21 PST 2009
Tue Feb  3 13:23:22 PST 2009
Tue Feb  3 13:24:12 PST 2009
Tue Feb  3 13:24:13 PST 2009
Tue Feb  3 13:24:14 PST 2009
Tue Feb  3 13:24:15 PST 2009
Tue Feb  3 13:24:16 PST 2009

Note the fifty second pause between 13:23:22 and 13:24:12? Ouch…