IP storage spans the WAN

Christopher Black immediately saw the attraction of IP transport for his storage applications. Black, network operations manager for investment and portfolio management company Effron Enterprises Inc., was looking to protect his data by replicating it from headquarters in White Plains, N.Y., to New York City, about 30 miles away.

He chose to use Gigabit Ethernet combined with conventional Fibre Channel. Spliced together in a new storage architecture called Fibre Channel over IP (FC/IP), the two technologies give Black the ability to send as much as 250G bytes of data per day over the WAN.

“We are replicating SQL Server data from a primary site to a remote hot site,” Black said. “The data we transmit consists of financial data for high-profile banks and financial institutions.”

Other network applications such as backup and recovery and data mirroring are increasingly relying on Ethernet transport to boost their reliability and scalability. Three storage protocols that use Ethernet are quickly becoming part of the network manager’s lexicon: FC/IP, Internet SCSI (iSCSI) and the Internet Fibre Channel Protocol (iFCP). All three operate on top of IP, whether it’s implemented as 1G or 10G Ethernet.

“The real benefit of the IP storage protocols is they don’t care what the underlying transport is,” said Tom Clark, technical marketing manager for IP storage vendor Nishan Systems. “IP storage is indifferent to whether the WAN connection is Gigabit Ethernet, SONET or point-to-point.”

Each protocol is being reviewed within the Internet Engineering Task Force (IETF) for standardization, which is expected later this year.

FC/IP is the most commonly used storage protocol in WANs and metropolitan-area networks (MAN). It is well-suited for mirroring data between geographically distributed storage-area networks (SAN) and is rarely, if ever, used as a transport for storage data across the LAN. In FC/IP, Fibre Channel frames are encapsulated in IP packets by FC/IP.

ISCSI encapsulates SCSI packets in TCP/IP wrappers. It’s most suitable for deployment in the workgroup to transport block-level storage data from Fibre Channel devices to workstations or servers, but you also can combine iSCSI with FC/IP or iFCP to link remote offices and data centers.

IFCP terminates the Fibre Channel session at the iFCP gateway and converts it to a TCP/IP session over iFCP. The destination gateway receives the iFCP information, initiates a Fibre Channel session, and converts the information back to Fibre Channel. IFCP is a good technology for users who want to preserve their Ethernet infrastructure. However, Nishan is currently the only vendor to offer iFCP products in its IPS 4000.

FC/IP and iSCSI can be implemented several ways over the WAN:

— As a stand-alone appliance, such as CNT’s UltraNet Edge Storage Router or Cisco’s SN5428.

— As a blade in a multiprotocol chassis, such as Cisco’s MDS 9500 Multilayer Director.

— As a port on a Fibre Channel switch, such as the Cisco MDS 9216 Multi-layer Fabric Switch.

Black uses EMC’s MirrorView application for replication with CNT’s UltraNet Storage Routers and EMC Fibre Channel Clariion storage.

The performance of the storage protocols is limited primarily by the capabilities of IP. Many storage applications can tolerate the 85-millisecond round-trip delay that speed-of-light latency causes in coast-to-coast transfers; but applications such as mirroring and replication of financial data typically require less than a 10-millisecond delay.

“The gating factor appears to be latency,” said Jamie Gruener, a senior analyst with The Yankee Group. “Packet-sizewise storage traffic is a lot heavier kilobytewise than traditional Internet traffic, which means to push it a longer distance is much harder to do. People generally are doing 100 to 200 kilometres or less.”

When putting storage over IP, consider the size and speed of the pipe and the distance data must travel. Nishan’s Clark recommends choosing a link speed based on the importance of the application you want to protect. To absolutely guarantee integrity of data, the more expensive synchronous methods might work well. But if an application can tolerate higher error rates, choose the faster but less expensive asynchronous transmission.

Brian Cobb, vice president of systems engineering for Fannie Mae in Washington, D.C., the third-largest provider of home mortgages in the U.S., relies on FC/IP to carry mission-critical underwriting data.

Cobb has between 1,200 to 1,400 servers in two geographically dispersed SAN islands. To join them, he chose FC/IP gear from CNT.

‘We were having some failures in the processes we were using for mirroring and replication,’ Cobb says. ‘We see good performance with asynchronous replication at a cost we can afford.’

Analysts say that for the time being, FC/IP will remain the predominant transport for storage over the WAN.

‘FC/IP is best suited to the WAN because it doesn’t alter the Fibre Channel protocol in carrying it over IP,’ Gruener says. ‘FC/IP is really about tunneling, which has lots of advantages when it comes to the security of data.’

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