Hi Dean,
The EonNAS is iSCSI connected and the way we are going to set it up is to create a disc pool for each server that needs backing up then present that pool as an iSCSI disk to that server.
I don't really grok the reasoning behind this topology. When it's iSCSI, it's LAN anyway, so it isn't an attempt to replicate classic SAN backup. Unless, of course, you have some dedicated iSCSI LAN with better throughput than the LAN, but that will have other issues (a lot of fun with multihomed hosts for instance). Then, having the disk for backup locally mounted to the backed up server is a recipe for disaster IMO. Any catastrophic system or admin failures that sink a server may also sink the backup with it. In addition, when you have to restore a server from scratch, there is no access to the File Library with the data, unless you manage to rehome it to some other MA host - which isn't as straightforward as you might think.
If I had to design a backup solution with the precondition "here is this iSCSI box, use it", I'd export a large LUN to my backup server which would also get equipped with more CPU than usual and with a mindblowing amount of RAM (think 128GiB or such). Then, I would put a StoreOnce Software store on that LUN and know my Advanced Backup to Disk Licenses are paying off on the dedup side, not the raw data (File Libraries are really outlandish when you look at the license costs vs. deduped B2Ds). SO writers auto-instantiate (with File Libraries its tedious hand work to create and configure them all to correct block sizes etc). SO can use source-side dedup to keep traffic from your LAN. Finally, you are tapping into HPs vision for federated dedup, which might come in handy in future extensions of your concept (like, say, bringing in a dedicated StoreOnce appliance or additional SO Software nodes, adding replication to another building or even site). I specifically mention this because
finally moving away from LTO2, 4 and 5 tapes
is a stance that I don't grok as well, on an even more fundamental level. Where is your backup? A single copy on some disk grave probably next to the source data in the DC is no backup. Even a single replica to a disk grave at another building gives me only light sleep. Tapes are not dead. They actually are so great because they are duplicating instead of deduplicating, and they are easily kept off-firecut and even off-site. And the great thing is: You don't need to backup to tape any more. Just copy from your SO store to tape, maybe twice, and good sleep comes back. This also allows you to have a shorter data protection on disk then you have on tape, so restores can initially get satisfied from disk and only need tape when you go back for more than e.g. a month. Best of both worlds.
HTH,
Andre.