IP storage on the WAN
Save it for the WAN
Fibre Channel may be more efficient for short distances,
but over the long haul, nothing is as practical as IP even if it's for functions
like disaster recovery. Here, we discuss the possibilities CIOs can explore
for SAN-SAN or SAN-NAS connectivity. by Deepali Gupta
The terrorist attack on the WTO twin towers in New York made people think about
the importance of backups and data mirroring. A series of natural calamities
followed, reinforcing the feeling that Disaster Recovery (DR) and multiple data
centres were imperative for the immunity of the business, because as they say,
'the show must go on.'
This is more so in a data-sensitive industry such as BFSI or BPO, where multi-location
data-centre-based operations are common. In manufacturing, SANs or storage locations
for the factory, branches and data centre can be far apart. Once the storage
is in place, the CIO's concern is to ensure that all the storage devices can
Exit FCP, enter FCIP
In the first phase of SAN evolution, Fibre Channel Protocol (FCP) was the only
means for a SAN to talk to another SAN or a NAS. However, pure fibre channel
was not feasible for three reasons.
The first was distance limitations; even though Brocade presently promotes native
fibre channel that can extend to 500 km, thanks to a newly launched switch family,
the standard distance that can be covered using fibre channel ranges between
40 and 60 km.
The second reason is the cost and difficulty in managing and laying fibre over
long distances. Not only is the initial cost of the fibre intimidating, but
because its tensile strength is low, it is prone to physical damage, particularly
in Indian conditions. Thirdly, the central section of the optical channel is
never a perfect cylinder. Signal leakage on account of light (signal) emitted
through the cable is a problem. While this loss is negligible over short distances,
over the long haul, it becomes significant.
A solution that would use copper for long-distance communication between storage
devices was required. As most companies already had connectivity infrastructure
in place, IP was the logical protocol to adopt for long-distance data transmission.
Nevertheless, FCP cannot be abandoned. Organisations had already invested in
FCP-compatible storage, and FCP was vendor-specific.
This was good news for vendors, because it meant a brand lock-in for any buyer.
As a result, like they had done with SCSI and iSCSI, vendors decided the best
way to deal with it was to encapsulate FCP in IP packets and transfer them using
the infrastructure for IP. This lead to the advent of Fibre Channel over IP
(FCIP) and Internet Fibre Channel Protocol (iFCP). Using WANs for storage data
transmission works for enterprises as their IT departments are already familiar
with IP and WAN technology. The TCO of an IP-based technology is lower than
FCIP or IFCP
FCIP can only be used to connect Fibre Channel SANs. iFCP maps FC onto IP, but
FCIP tunnels data over IP. This makes FCIP a higher bandwidth consumer.
FCIP encapsulates a FC frame within an IP packet quite like IP encapsulates
an Ethernet Frame. It is simple and can be implemented in standard switches
and routers. On the other hand, iFCP is a gateway-to-gateway approach. Here,
the FC frames are mapped into IP packets through the first gateway, and the
reverse takes place when the IP packets are received.
In the iFCP market, McData is the only player through its acquisition of Nishan
Systems. FCIP-enabled products are available with a number of vendors. See Table
'FCIP/iFCP available in the market.'
Cause for concern
Reliability of WAN for critical data transfer such as disaster recovery will
be a cause for concern for most CIOs. In addition, these are bandwidth hogs,
which means that most mid-sized enterprises will need to invest in additional
According to Sanjay Kharade, Principal Consultant, Cisco
Systems, India and SAARC, "Traditional TCP has a tendency to overreact
to packet drops. As a result, reduction in speed or throttling back that occurs
is unacceptable to storage traffic." These issues, however, can be dealt
The TCP stack can be optimised to carry storage traffic, by adjustment of parameters
such as window size, maximum bandwidth, minimum available bandwidth, round trip
time and congestion window monitor burst size, Kharade suggests.
One way to ensure WAN reliability is to incorporate a WAN
accelerator device. B Chandrashekar, Country Manager, India, Intransa says,
"These devices manage WAN band width utilisation to improve performance
and different flavours, and provide compression."
|Brocade SilkWorm Multiprotocol Router AP 7420
||The FC-FC Routing Service permits devices located in separate
SAN fabrics to communicate without requiring the fabrics to merge into a
single large SAN. FCIP tunnelling service helps organisations extend their
FC SANs over distances that would be impractical or expensive with native
|SilkWorm 4100 Switch
||This FC switch can be used to link up storage set-ups as far
as 500 km apart.
|Network Appliance gFiler Gateway
||These gateway products support Hitachi Freedom Storage Lightning
9900 V and 9900 series and the Thunder 9500 V series storage systems, the
IBM TotalStorage Enterprise Storage Server (ESS) series and DS4000 series,
HP StorageWorks XP Disk Arrays, Hitachi Japan SANRISE systems and SUN StorEdge
|McDATA Eclipse 4300 SAN Router
||It uses IP, Gigabit Ethernet (GbE) and Fibre Channel (FC)
for wire-speed storage fabric connectivity with IP-based LAN, MAN and WAN
routers, and switches.
|HP StorageWorks B-Series
||FC-FC Subnet Routing Service for SAN island consolidation,
||FCIP tunnelling service for SAN extension (distance-connectivity)
fully integrated with Continuous Access (CA) solutions for EVA and XP product
families, iSCSI Gateway Service for sharing FC storage with servers on IP
|Cisco Fibre Channel over IP Port Adapter Interface for Cisco
7200 and 7400 Series Routers
||It provides networking services such as data compression,
encryption, access control lists, firewalls and quality of service using
Cisco IOS Software and can be used to extend a SAN over an existing IP (WAN)
Why use FCIP
FCIP has some significant advantages. It is an IETF standards-based protocol
and it preserves the FC infrastructure that a company may already have invested
in. It is transparent to all existing FC applications and it leverages the widespread
reach and economics of IP networks that include E1 and E3 networks. For more
information on the various new aspects to storage data transmission that IP
has brought in, refer to box 'Opening new doors.'
While some vendors believe the trend of using IP to connect storage devices
such as SAN and NAS has already caught on, others like P K Gupta of EMC believe
that the technology is "still in infancy, and finding it hard to make a
mark in the enterprise set-up." Nevertheless, FCIP and iFCP hold substantial
potential for CIOs who want to squeeze the last dollar from their storage investments.
Deepali Gupta can be reached at