ESXi Accessing LUNs: Physical or Virtual Mode

Your plan is not nuts. As usual, there's more than a few ways to attack this based on what you're trying to achieve and how to protect your data.

First up, you can present a raw LUN to a VM using a "Raw Device Mapping". To do this:

• Present the LUN to the ESXi host (or host group, if you are going to use clustering/HA)
• Add a disk to your VM, select Raw Device Mapping, point at the LUN
• Rescan the SCSI bus inside the VM
• fdisk, mount and add to fstab, just like a normal disk.

Upside: fast to set up, fast to use, easy, can represent the disk to physical host if you find yourself needing to V2P down the track

Downside: you may lose some VMware-based snapshot/rollback options, depending on if you use physical or virtual compatibility mode

An alternate option is to create VMFS on the LUN to create a datastore, then add a VMDK disk to the VM living on that datastore.

• Upside: it's Storage vMotion-friendly if you ever buy a license to use it. This allows for hot migration of VMDK disks between LUN's and even SAN's.

In both cases, you're in a similar risk position should VMware or your VM eat the filesystem during a failure; one is not drastically better than the other although what recovery options will be available will be quite different.

I don't deploy RDM's unless I have to; I've found they don't buy me much flexibility as a VMDK (and I've been bitten by bugs that made them impractical when performing other storage operations (since fixed - see RDM section in that link))

As for your VM, your best bet for flexibility is to store your fileserver's boot disk as a VMDK on the SAN so that you can have other hosts boot it in the case of a host failure. Using VMware's HA functionality, booting your VM on another host is automatic (the VM will boot on the second host as if the power had been pulled; expect to perform the usual fsck's and magic to bring it up as in the case of a normal server). Note, HA is a licensed feature.

To mitigate against a VM failure, you can build a light clone of your fileserver, containing the bare minimum required to boot and have SAMBA start in a configured state and store this on each host's local disk, awaiting you to add the data drive from the failed VM and power it on.

This may or may not buy you extra options in the case of a SAN failure; best case scenario, your data storage will require a fsck or other repair, but at least you don't have to fix, rebuild or configure the VM on top. Worst case, you've lost the data and need to go back to tape... but you were already in that state anyway.

I'm currently thinking about upgrading my VMware 1.04 to Version 2 - but I use physical devices for my virtual machines right now. I've noticed a huge performance difference between virtual and physical disk drives.

The new VMware Server User's Guide tells me not to upgrade: "VMware Server 2 does not support physical (raw) disks." (p.44) - this should answer your question, too..