What hardware changes are needed?
Adopting iSCSI currently means installing an iSCSI router to connect an Ethernet LAN to a Fibre Channel SAN, and this approach will likely continue for six to 12 months, Bragg suggests. These routers are typically a fibre switch fitted with one or more Ethernet ports for iSCSI. Bragg stresses the importance of carefully estimating the aggregate bandwidth needed for a project of this kind, as the throughput of such devices varies from around 50Mbps to 120Mbps. "Scoping is the absolute priority," he says. Since iSCSI is such a new standard, it is also important to check that the router and storage vendors have certified the interoperation of the selected products.
HK Tan, marketing manager at Adaptec Asia Pacific, agrees. Interoperability has been "plagued with a lot of problems," he says. Glynne is more optimistic, saying extensive industry experience with IP means it is unlikely there will be many interoperability issues.
The current roadblock in the adoption of iSCSI is the lack of storage units with suitable interfaces, according to Bragg. He says major storage vendors are looking at providing gigabit Ethernet interfaces on disk arrays and tape libraries by 2003. Gelbart concurs, predicting large-scale deployment of the technology by 2003 or 2004 without making any comment about the likely availability of products from EMC.
You get a different story when you talk to IBM. Glynne points out that IBM started selling iSCSI storage last year, including the TotalStorage IP Storage 200i appliance offered in capacities from 108GB to 1.74TB.
Another performance issue concerns the throughput of the network interface cards (NICs) fitted to the servers. It is possible to use free iSCSI drivers with many recent-model NICs, and the performance may be adequate for file and print servers. Application servers may not have enough processor power to spare, in which case an enhanced NIC with a TCP/IP offload engine (TOE) is called for. At present, TOEs are similar in price to Fibre Channel adaptors, but Bragg expects their price will fall. He recommends organisations test the difference in performance between a normal NIC and a TOE in their own environments before making a decision.
Tan says Adaptec's ANA 7711 network accelerator card (yes, that completes the trio of NIC, NAC, TOE) with copper or optical interfaces would be in beta testing by the end of the year. Benchmarks show gigabit Ethernet can consume up to half of a server's CPU cycles, and moving this function into an ASIC on the network card can deliver a significant performance improvement. TCP/IP offload becomes more advantageous as the throughput increases, he says. "It allows you to scale linearly."
Quantum has held back iSCSI support in its storage products pending finalisation of the standard and the availability of TOE adaptors. The company has provided this feature to selected customers for over a year, and expects a general release shortly, according to Mike Sparkes, Quantum SSG APAC product marketing manager. Existing Ethernet storage libraries can be given iSCSI capabilities through software upgrades, he says, but TOE adaptors are needed for performance reasons. Quantum has given a proof of concept demonstration by backing up servers in Israel to storage devices in California, though the company wouldn't recommend this approach for everyday use, he says.
Network Appliance is already shipping a proprietary implementation of iSCSI for its Filer NAS units, according to systems engineer Steve Bracken. "It's just another protocol" for accessing information stored on a Filer, he says. When the standard is finalised, the Filer software will be made compliant and all an owner would need to do is replace the existing server NICs with TOE adaptors and pay the licence fee to activate iSCSI support in the Filer. Data already stored on the Filer will still be accessible, he says.
If all or most of your servers are located in a single room, iSCSI traffic can be carried over an Ethernet that is isolated from your main network. But if the object is to connect dispersed servers to a storage farm, it is likely that SAN traffic will flow over the general purpose LAN. This extra traffic is very bursty, and so its impact on the rest of the network must be considered ahead of time.
Separate network segments for iSCSI are the way to go, according to Tan. He argues that part of the attraction of SANs was to isolate backup and other traffic from the rest of the LAN. iSCSI allows the construction of a IP "cloud" connecting servers and storage devices, "just like the Internet cloud" connecting servers and clients.
Simon Elisha, senior systems engineer at Veritas, says some people argue that given the segmentation of purpose between a LAN and a SAN, you might as well use different pipes for each purpose. That can be done logically rather than physically, but how well that works depends on the exact requirements and the technology being used. Either way, network managers must understand the implications of putting SAN traffic onto the main network.
In Gelbart's opinion, organisations that have already installed Fibre Channel SANs are unlikely to consider converting to iSCSI for at least three or four years, though they may add iSCSI to their SANs to gain the advantage of consolidated storage across a wider range of servers.
But iSCSI opens up a potentially large market for organisations that couldn't previously afford a SAN. Tan sees the emergence of "a mini-SAN market for customers with half a dozen servers." Such organisations typically have no Fibre Channel expertise, but iSCSI uses standard and familiar protocols, and offers proven reliability and ease of network management, he says.
"It'll be a saviour for small- to medium-sized businesses," says Sparkes, while Bracken says "there's a big sweet spot there" for connecting consolidated storage to Windows application servers (such as Exchange Server and SQL Server) that aren't subject to extremely high workloads.
Some people think iSCSI will find a place in big businesses. Many top tier Australian organisations have delayed moving to SAN, says Elisha, and iSCSI provides them with an alternative to Fibre Channel.
Will it be possible to add iSCSI interfaces to existing storage units? The vendors we spoke to wouldn't give a definitive answer, but most of these devices are fitted with modular interfaces to accommodate various network architectures. "Potentially, there will be an iSCSI card," says Gelbart, in which case the storage devices will be connectable directly to an IP SAN rather than via an iSCSI router.
But storage isn't only about hardware. "You need to make sure your software will work with iSCSI," says Elisha. There are plenty of low-level issues that can cause problems, he says, but Veritas has validated its Volume Manager, NetBackup, and SANPoint Control products against the Cisco 5420 router often used to link iSCSI to a Fibre Channel SAN. With the right management software, the administrative impact of introducing iSCSI should be minimal, he suggests. iSCSI is "exciting from a plumbing perspective, but our goal is to make it boring from an application perspective," Elisha says.
At the end of the day, organisations are interested in business continuity and business efficiency, Glynne says. iSCSI can play a part in disaster recovery by enabling long-haul storage connections, as well as presenting an attractive TCO proposition.
"It's a matter of the end user seeing the business benefits," says Sparkes.
