Why has ESXi 5.0 not used the software RAID configuration on my test server?

Question

I've got a test server which was running WS 2008 Enterprise on the bare metal. It was correctly using the software RAID 1 configuration (2x250 GB disks which appeared as one disk), setup on the Dell Poweredge T110 (which meets compatibility requirements) without requiring any extra setup from me. (As an aside I'm fairly sure it's software RAID, as we didn't spec a hardware RAID controller, if that's of any importance in this situation).

I am now testing installing ESXi 5.0 on this server to run some VMs. I've successfully installed ESXi, and imported a VM fine, but it's showing 2 x 250 GB disks available as datastores. However they should be appearing as one volume. When I boot the server, there is a RAID configuration screen you can enter, and I'm guessing this is what I'll have to do at some stage, but now need to be very careful because there is one disk which contains data that I want to be mirrored on the other disk. What is the best thing to do in this situation?

Solution

This is very simple - you have two 250GB disks that are presented to any OS as two disks, that you'd configured Windows to mirror them is nice but irrelevant as they were always two disks. ESXi is just seeing the same two disks and as it doesn't support software RAID is just showing you the two disks as they were presented to it.

Of course there's nothing to stop you creating two .vmdk's, one per datastore, attaching them to a VM and having that VM's OS mirroring them internally - at least then it will handle the failure of the disk that's not got ESXi running on it. Bit pointless and you should just get a RAID-capable and HCL-approved controller but there you go.

Comments

[Zoredache]

Buy a better RAID controller that is on the HCL. ESXi is very picky about hardware. Which controller does that box have by the way?

[kafka]

it's software. I understand that ESXi won't work with software RAID in the same way, so I'm either looking at a workaround using RAID within the VM OS, or getting a hardware controller, or just not using software RAID in this instance.

[Robin Gill]

As it's only a test server, I would pop over to ebay and look into perc 5i /6i cards with battery backup.

[kafka]

OK thanks for the swift response. If an approved hardware RAID controller is the way to go I guess the best thing would be: clone the VM; install the controller; reinstall ESXi and import the VM?

[kafka]

As an aside, I don't recall explicitly telling Windows to mirror the disks, it just took care of it on its own!

[Alex Berry]

Windows will never mirror disks on it's own. You need to convert the two disks to dynamic and then create a mirror, if you didn't do that then you were just very lucky to have never needed the mirror!. If there is a raid configuration screen you should utilise this prior to esxi install, reinstall it, then you will see a second datastore.

[Robin Gill]

To me is sounds like kafka is using either Intel matrix RAID or PERC S100, has set the mirror up in the RAID card option BIOS. This RAID is recognised by Windows, but ESXi just sees the seperate drives.