I'm trying to create my own SAN out of existing hardware. I have four identical NAS devices. Each one has four 1 TB drives that they do RAID-5 across. On each NAS I have created a 1 TB iSCSI share. I have another linux server that connects to each iSCSI target. On this server I have created a RAID 10 array of these iSCSI devices. I then plan to share this array out via NFS. With this setup I could survive several hard drive failures and even lose a whole NAS. But I also want to have a second NFS server as well. It sounds like my second server should be able to connect to the iSCSI targets without a problem but I'm not sure what will happen when I try to create the RAID 10 array.
While this is an interesting approach, I believe you are correct in realizing that the software RAID-10 won't work when you try to extend it to another server. Instead, I think you'll need something like DRDB or GlusterFS to achieve your goals (or possibly both, and/or a clustering filesystem like OCFS2 or GFS).