Yes, we use it as iSCSI solution. I think it also supports FC.
Their new version of the OS uses ZFS as backend, but we havent deployed that yet, since we'd like to see site-resilience working with that setup first.
While we're throwing out suggestions ... Have you had a look at Open-E's cluster setup?
It's basically DRBD, but then supported.
I've been running it as redundant backing for VMware, because it's supported by them too. Rock solid!
Refusing allocation of a tty usually happens on two occasions:
1) All available tty's are busy: This may happen when many terminal sessions are running
2) Your server is completely out of memory: Too many VM's allocated?
As for 1) ... see if you can create more tty's. A google for "udev tty...
As part of the community repository offering, running proxmox on a minimal jessie install, I upgraded my proxmox to kernel 4.2.8 as it became available.
Only recently I found out (during a reboot when the new kernel became default) that for some reason, booting from an mdraid0 boot device...