RHEV  stores virtual machines on a specific type of storage domain, the so called “data domain”.

While creating a new iSCSI data domain you need to perform these steps:

1. Set the host used as iscsi initiator, the IP address/port of the iSCSI target.
2. Eventually add the credentials to perform a CHAP authentication.
3. Discovery and login to a particular iqn.
4. Expand the LUNs lists shown by the GUI and select the LUN/LUNs that you want to add to the data domain.

Note that the GUI will show you only the un-initializated LUNs discarding pre-formatted or too small LUNs. This is done intentionally but not explicity in order to avoid the risk of overwriting existing data.

If you want to force RHEV to use a LUN with existing data you can wipe out at least the first 512 bytes of the LUN to convince RHEV that the LUN is empty by executing this simple command:

# dd if=/dev/zero of=/dev/mapper/lun_name bs=1M count=10

The value of 10M is arbitrary but feel free to choose another value.

Now perform a new cycle discovery+login and the GUI will show you the LUNs!

And now a question for Red Hat developers: hey guys, why don’t you show a simple alert???

P.S. On #rhev we found that this behaviour will be modified with 3.1 release: administrator will see the unselectable LUNs also ;-)