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Crossing the Channel: What IP can do for storage
"...a potent source of growth for the networked storage market", according to one analyst house

By Anthony Plewes

Published: Tuesday 02 September 2003

IP is boosting the distance limitations of traditional storage networking technologies, claims Anthony Plewes. So what exactly should IT departments expect?

The increasing use of business critical applications such as CRM and ecommerce software has propelled data storage issues to the top of the IT agenda. Many companies are having to look very carefully at where they store this information and how safe it is in the event of a disaster. Reassessing their storage and storage area network (SAN) requirements has become a priority.

Fibre Channel (FC), the dominant communications technology for SANs, is increasingly under the strain of distance. Generally, FC is run over a dedicated network to a storage centre, with a maximum radius of 10km. However, new business continuity, disaster recovery and rationalisation strategies are demanding more from FC. Many companies want storage much further away from a potential disaster zone, as well as rationalising enterprise data storage into two or three global locations.

Until recently, Fibre Channel has been the only networking technology ideally suited to storage, with speeds between processors and disk arrays of 1 or 2Gbps. Ethernet could generally only support 100Mbps and over shorter distances – not ideal for a storage technology. Faster and better communications technologies are now coming to storage networking to boost FC's distance or even replace it altogether.

For instance, FC over optical technologies such as wave division multiplexing (WDM) can mean distances of nearly 200km. However, WDM is limited to metro areas and for some companies 200km is simply not far enough.

“Many large corporates want to consolidate their data centres to as few as three across the globe,” says Ian Bond, business development manager for storage at Cisco. “This means that replication and backup has to work over very large distances.” Companies also want to have copies of their business-critical information well away from any possible metropolitan-scale disaster.

Size is important

The most common approach to extending the reach of SANs is to utilise IP. The Fibre Channel over IP (FCIP) standard has been around for nearly two years and it has already been proven to work over substantial distances. For example, Cisco, Hitachi Data Systems and Sprint successfully tested replication over a distance of nearly 6,000km.

While this trial was carried out in laboratory conditions, Bond claims that many of Cisco’s customers already use FCIP for replication between distant data centres. For example, Cisco customer AXA Life uses FCIP over a link between its Paris and London data centres, and even has a back-up link via Amsterdam which stretches over some 1,500km.

Handling massive distances such as these is no trivial task, says Bond, even if delays for large distances can now be in the millisecond range.

Companies are using FCIP for remote backup applications, because the FCIP standard is not suited for synchronous replication over distance, simply because the delays are too large. Corporates will use a mix of technologies for their SANs, including both FCIP for daily remote back-up for disaster recovery purposes and FC over WDM for metro area synchronous replication, so that the company can call on two sets of data in case of smaller failures.

“The storage traffic requirement is massive,” says Derek Granath, director of hardware products at leading SAN switch vendor Brocade. “We are talking about entire Oracle databases in the region of 100 gigabytes. Companies have requirements for backup of 100 terabytes – this needs a very big pipe.”

A new animal

FCIP is not the only area where IP is making an impact in SANs. Some quarters are announcing the emergence of a new animal called IP-SAN based on the iSCSI standard. Many in the industry argue that calling storage networks based on iSCSI, IP SANs is misleading and many vendors desist from the term. iSCSI can also boast the backing of Microsoft, which released drivers for XP and Windows 2000 in June 2003.

iSCSI takes the storage command directly from server and transports it over IP to the storage device. However, the performance of this approach is limited and it is in no way meant to replace SANs based on Fibre Channel. It is targeted at the low end of the market.

“iSCSI is a way of extending the core SAN out to the IP network to include low-level servers which are not typically included in Fibre Channel implementations,” says Cisco's Bond.

This should open up SAN functionality to a whole new generation of servers. According to Gartner Dataquest, by 2006 iSCSI will connect nearly 1.5 million servers to SANs, making it the most widespread SAN technology.

The key strength of iSCSI is that it uses the standard NIC card for the processing but this limits the performance because of the extra processing that the standard requires. “This is leading some vendors to handle the processing with extra hardware,” says Brocade’s Granath, “But this means it is no longer a standard NIC card and hence not as cheap a solution.”

iSCSI will attach to the FC-based SAN through gateways. Vendors are addressing this by including iSCSI and FCIP support in their SAN switches. The Yankee Group has identified entry-level IP storage arrays as a potent source of growth for the networked storage market and will shift the market from mostly Fibre Channel SANs to IP storage systems.

Service providers return

The emergence of IP technologies in SANs is also tipped to revive the fortunes of the ill-fated storage service providers (SSP). The latest wave of SSPs offer storage services and back-up and customers should be able to plug their Fibre Channel stream to the box - which would go over distance using IP - and at the far end the carrier would translate this back into Fibre Channel and into the disk arrays.”

IP, married to SANs, is opening up new business models for service providers and new options for user organisations.