The market perception seems to be that iSCSI is gaining tremendous steam and many customers who would have adopted Fibre Channel as their interconnect a year ago are now adopting iSCSI. I would agree that this is the case but iSCSI is not an emerging interconnect and might be better classified as a legacy interconnect which is now experiencing a newsworthy adoption rate. An early concern of iSCSI was the performance penalty associated with TCP operations and the impact of software based initiators, this spawned the TOE (TCP Offload Engine) which would offload TCP calculation from the system CPU to a dedicated onboard processor dedicated to TCP operations, today most iSCSI implementations leverage software initiators (today system CPU resources the most part are so under utilized that most environments will never notice a 10% CPU utilization increase that may be associated with iSCSI). Some vendors addressed the TCP concern by modifying the iSCSI protocol to ride on UDP as opposed to TCP thus increasing performance via proprietary protocols which resemble iSCSI (i.e.- LeftHand Networks, HammerStorage and Zetera). It is important to note that LeftHand has pretty much abandoned the proprietary protocol they started with and has now adopted the iSCSI standard, it is also interesting to note that their adoption rate seems to have increased since doing this, when you are a new player I think evangelizing your protocols superiority over the standard is probably a tall order. LeftHand has also changed morphed their business into a software play and embraced the VMware Virtual Appliance Markerplace as a way to propagate their technology.
There are a number of emerging interconnects that technologically out shine iSCSI the question is how quickly can the market makers move to adopt these technologies, are the market makers interested in accelerating the adoption curve? This is a complicated question, on one hand you could argue that technologies are more stable once they have been around longer (I remember reading papers on iSCSI in 2001, did it really take 7+ years to get iSCSI to where is today?) on the other hand if the market makers validate these technologies too early they run the risk of fierce competition from more nimble startups. It is a complex problem, my feeling is that for the most part the adoption cycle is slowed by the market makers as a way to recoup development cost and and slow competition. IMO the by product of this is a slower innovation cycle.
AoE and HyperSCSI both offer the interconnect price point of iSCSI without the performance burden associated with TCP. AoE and HyperSCSI ride on Layer 2 and do not experience the protocol overhead associated with Layer 3 protocols. SoIP (Storage over IP) uses UDP as the transport protocol as opposed to TCP. We are also seeing the emergence of iSER and iWARP, next generation TCP technology that closely resembles Infiniband. iWARP (Internet Wide Area RDMA Protocol) is a superset of the VI architecture and is aimed at reducing the overhead associated with TCP, iSER (iSCSI Extensions for RDMA) maps the iSCSI protocol over RDMA networks like Infiniband or iWARP. iSER address the overhead associated with TCP and out-of-order packet delivery. How many of us hear about these protocols?
It seems that the majority of marchitecture effort is being put into FCoE (Fibre Channel over Ethernet). Major players such as Brocade, Cisco, EMC, Emulex, QLogic, IBM, Intel, Sun and Mellanox have all gotten behind FCoE in a big way so most likely this will be the next big thing in storage interconnects. The emergence of technologies that further leverage Ethernet as the interconnect will change the game, it is hard to imagine that Cisco’s dominance will will not continue to grow. It is likely that more storage services (i.e. – replication, snapshots, etc…) will be handled at the network layer, as these services move into the network layer we will continue to see the further commoditization of the storage market. Should be interesting to watch over the next few years.
While on the surface protocols that sit on top of Layer 2 (AoE and FCoE) may seem to be superior there is a tremendous amount of functionality that is provided at Layer 3 so it is not a forgone conclusion that FCoE will will the battle. Right now the only forgone conclusion I can see it that Cisco wins regardless, the others will be battling for a piece of the pie. But who knows anything can happen, after all this is technology.