Don’t use the Microsoft iSCSI Software Initiator in a Virtual Machine

Lots of people regularly use the Microsoft iSCSI Software Initiator on physical machines to attach iSCSI LUNs from filers to hosts. This is an add on free download for Server 2003, and comes pre-installed on Server 2008.

 In general, on physical machines, it works fine.

So assuming that it’d work just fine on a virtual machine, we tried to use it on some production machines running Small Business Server 2003.  It seems to load just fine, and works like it usually does on a “real” machine – *BUT* it has terrible throughput under load.  It’ll even disconnect at random times.  Uninstalling/reinstalling, and lots of fiddling around didn’t help.

Of course, we went to Google to see if others have issues with it, and there’s *LOTS* of whining about this, both on VMware ESX and XenServer.

It’s possible that it has been addressed in Server 2008.  We saw this on 2003, and haven’t attempted to replicate the issue on 2008 vm’s.

Nonetheless, we suggest you figure out another way to attach iSCSI LUNs from a filer to a Windows virtual machine.  Both ESX and XenServer allow you to easily present iSCSI based disks to vm’s inside their virtualization environments.  Don’t do it with the Microsoft iSCSI Software Initiator from within the guest.

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