Multiple LUNs on one iSCSI target vs multiple iSCSI targets

I need advice on the difference between having multiple LUNs on one iSCSI target hosted by a ReadyNAS Pro vs having multiple iSCSI targets with one LUN each. Currently, I have a VMware ESXi box running my Cisco lab servers. One of those voice servers is hosted by the ReadyNAS as an iSCSI target with one LUN. I also have another iSCSI target with one LUN configured on the ReadyNAS and used as a non-system disk for a Windows XP VM. The system disk of that VM is hosted in a local ESXi datastore.

Last weekend, I upgraded from ESXi 4.0 to ESXi 5.0. During the upgrade, I was asked something about changing some kind of VM IDs or keeping them the same. I chose to change them, and since then my Cisco voice server (with the datastore on an iSCSI target located on the ReadyNAS) can no longer be started even though I can browse that datastore. The Windows XP's (non-system) disk (which is another iSCSI target on the ReadyNAS formatted as FAT32) survived this upgrade to ESXi 5.0.


I am no expert in iSCSI or storage solutions by any means, so I am asking expert advice here. I am going to upgrade to RAIDiator 4.2.19 (hopefully later this week) and see if my Cisco voice server hosted on the ReadyNAS will start working again. If it does not, I will have to wipe that LUN out and start from scratch. I have recently expanded my storage on the ReadyNAS, and I am thinking about hosting my entire Cisco lab off the ReadyNAS. So, my question is about how I should create datastores on the ReadyNAS. Should I have just one iSCSI target and create a new LUN for each VM, or should I create a separate iSCSI target for each VM? What are the pluses and minuses of either approach?

Thanks!