A common point raised when comparing iSCSI to AoE protocols is that AoE is not routable and therefore not satisfactory for Enterprise use where there may be many sites between which you wish to share data. In fact this feature is what lead to the development of iSCSI in the first place.
This is true in that AoE is a light layer 2 protocol integrated with Ethernet frames, and therefore by definition it is stopped when it meets a router. This provides security in that data cannot inadvertently be routed out of the network but also causes a headache when it needs to be routed away from a common LAN segment, with DR being a common requirement needing this feature.
Because AoE does not have a built in authentication method like iSCSI, and can only secure data with LUN to MAC address masking, it would also be a risk to expose the data to any external network directly.
Coraid have their own solution for this, which requires placement of a AoE gateway at the LAN segment edge before the router, which can then route encrypted AoE packets over IP to another gateway on another network. This works great over IP but is vendor specific, so what if you like the idea of AoE but want a more generic solution – AoE is Open Source after all?
In research at University College Dublin, they found that AoE over MPLS provides a routable protocol which can be implemented without a need for tunnels, and with a very modest increase in the header size in comparison with raw AoE. As a side benefit, the resulting protocol is no longer restricted to Ethernet, because MPLS runs over whichever mix of networking technologies it faces – including ATM, SDH, Metro Ethernet, etc.
All this extra flexibility comes at just a 12% overhead over the raw AoE protocol, still putting it way below iSCSI. This is a significant piece of research work and could significantly change the playing field for AoE as a diverse storage protocol for the Enterprise.
For the full research paper download the PDF from the UCD site.
Millennia Blog 