We have come across a curious issue with degraded or unresponsive NAS mounts within a VM (RedHat 4 32-bit) when it is hosted on ESX 4.1 that goes away when the VM is migrated to an ESX server running ESX 4.0 U2. We have opened a case with VMware.
The VM has two NAS mounts and executing a simple 'ls' command on the mount point or a 'df' command will hang uner 4.1. The odd part of it is that we cannot reproduce the problem on our internal test VMs, mounting the exact same NAS devices. So in summary the problem is only reproducable on certain VMs but is always caused by migrating to ESX 4.1 and fixed by migrating to ESX 4.0 U2. Migration itself does not fix it, for example going from and ESX 4.1 server to another ESX 4.1 server does not fix it and migrating from ESX 4.0 U2 to ESX 4.0 U2 does not cause it.
It appears to be something about how these particular VMs interact with 4.1. We thought turning off IPTABLES within the VM helped, but that is not consistent. We are currently working with a clone of one of the problematic VMs so that we can strip it down to the simplest level that still causes the problem.
