one nas two servers - how best to make proxmox failover cluster?

Hi all

I have a:

Synology DS 1513+

and 2 servers ...

How do i best make a cluster?

I was planing in the begning of just using ISCSI but than i learned that that would mean i couldn't do backups...

than i figured NFS but that doesn't seem to be supported..?

I have heard about something with a 3 node cluster where you could do some ISCI or NFS?

all in all my impression is that making a proxmox failover cluster with only one nas and two nodes is vary hard?

PLEASE set me streight???

my proxmox version is 3.1-3/dc0e9b0e

Thanks

Casper