ESXi not accepting previously used volume

I recently had a problem on an ESXi 5.0 box I was trying to add a iscsi target to. I had set up a 6 TB  iSCSI LUN but everytime I tried adding it to ESXI I got the following error:

Call "HostDatastoreSystem.QueryVmfsDatastoreCreateOptions" for object "ha-datastoresystem" on ESXi "ESX HOSTNAME" failed. 

It turned out that the setup wizard on the device had happily created a volume and formatted it with ext4 before I realised what it was doing. Although I removed this volume the partition information wasn't removed from the array and this was upsetting ESXi.

How do you fix it? As there was no obvious way to wipe the partition info from within the Array's management interface I decided to do it from a Debian VM running on that host.

Firstly I removed the discovery information from the ESXI server so it isn't trying to interfere then on the Debian VM I installed open-iscsi with:

apt-get install open-iscsi

Start the open-iscsi daemon with:

/etc/init.d/open-iscsi start

Query the iSCSI target on the storage device:

iscsiadm -m discovery -t st -p 192.168.1.99

Which should return something like this:
192.168.1.99:3260,0 iqn.2010-12.com.manufacturer:nasdevice.name

If you have set up iSCSI authentication on your storage device you will need to run something like the following commands using the iqn in the above response.

iscsiadm   --mode node  --targetname "iqn.2010-12.com.manufacturer:nasdevice.name"  -p 192.168.0.99:3260 --op=update --name node.session.auth.authmethod --value=CHAP
iscsiadm   --mode node  --targetname "iqn.2010-12.com.manufacturer:nasdevice.name"  -p 192.168.0.99:3260 --op=update --name node.session.auth.username --value=username
iscsiadm   --mode node  --targetname "iqn.2010-12.com.manufacturer:nasdevice.name"  -p 192.168.0.99:3260 --op=update --name node.session.auth.password --value=password

Logon to the storage device:

iscsiadm -m node --targetname "iqn.2010-12.com.manufacturer:nasdevice.name" --portal "192.168.0.99:3260" --login

All being well this should now create a SCSI device as if you had attached a hard drive directly to the system. I looked at the bottom of the output from the dmesg command to find out which device (/dev/sdb).

I used the following command to write zeros to the first half a MB of the disk which will overwrite any partition table information (care should be taken that you have the correct device when using this command, it will eat your drive):

 dd if=/dev/zero of=/dev/sdb bs=512 count=1024

Now logout of the storage device with the following command:

iscsiadm -m node --targetname "iqn.2010-12.com.manufacturer:nasdevice.name" --portal "192.168.0.99:3260" --logout

ESXi should now happily accept the iSCSI LUN when you attempt to add it.