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it was LAN. Then WAN. Now it could be storage area networks, or
simply SAN. The concept of network storage, existing from the punch
card days, is just beginning to crystallize into a mature technology.
SAN
sensation
SAN, on the other hand takes off where NAS ends. Unlike NAS, which
builds on an existing network, SAN explores the possibility of establishing
an exclusive network for storage. Speed, sharing, storage consolidation
and inter-operability being some of the primary objectives of SAN,
it attempts at centralizing storage on a dedicated network to enable
inter-connect between servers and storage systems. Technically,
IBM defines a SAN as a "dedicated high-speed network of directly
connected storage elements designed to move large amounts of data
between host independent, distributed storage devices. Ownership
of the storage resources are 'de-coupled' from the servers."
Essentially, this is achieved through disk virtualization, wherein
physical capacity can be pooled across the enterprise for presentation
to applications servers.
A
SAN is generally opted by organizations where data storage becomes
critical and has a direct bearing on the business performance. The
Bombay Stock Exchange (BSE), for instance, has already gone in for
implementing SAN in a phased manner in order to deal with the online
transactions involving crores of rupees per day. The company's decision
to go in for SAN was triggered by its need to consolidate the flow
of data for its BOLT (BSE Online Trading System) and BOSS (BSE Online
Surveillance System) projects.
For
Jet Airways, a private airline company, the tough fight it has to
put up in the competitive market, is making it consider options
of network storage. Says VP Badri Narayan, GM, Communications and
Automation, Jet Airways, "We are considering various network
storage options for the long run. This is because of the mission-critical
applications that drive our business." He should know, because
a server downtime of just one hour results in a Rs5 lakh loss, at
an average of about 100 tickets booked at Rs5,000 each, across different
destinations in India.
Opting
for SAN
"With privatization and competition setting in, even quasi-government
establishments such as LIC are considering holistic storage options
for running their businesses. Having the world's largest number
of insurance policy holders, LIC is eventually considering SAN type
of solutions to store, back up and manage its voluminous data in
flow," says Princy.
"Worldwide, the storage market is willy-nilly moving in the
direction of SAN. SAN is showing the greatest growth among the various
connects. Other connects will still stay.
However,
for most business critical applications, major users will move the
SAN way," says Owais Khan, GM, Storage Works, Compaq India.
In addition to strategic strengths, SAN offers economies of scale
as the network storage servers are shared among many application
servers. This way the enterprise can get storage in bulk and apportion
it to their users as needed. Distributed servers and storage can
be transformed to consolidated storage systems, while separate islands
of information can be turned into consolidated enterprise data with
the help of a SAN. SAN offers an enterprise the ability and agility
to continually adapt to changing market requirements. More importantly,
SAN eliminates manual backup processes and offers high-speed data
access because it is inter-connected with fiber channel.
Components
of SAN
Till a few years ago, the SAN initiative continued to be making
modifications on the hardware and connectivity end. Today with varied
technologies in play, SAN has hardware, software, solutions and
services, inter-connect, and implementation architecture areas that
have been continuously addressed for better support. The most revolutionary
progress has been made in the network interconnect technologies.
From SCSI (small computer system interface) to fiber channel, the
transition has addressed high bandwidth at low latency, extending
to longer distances. For even SCSI, the dominant interconnect in
almost 90% corporate storage has the limitation of reaching upto
just about 60 meters at the rate of 40Mbps. While the long and skinny
ethernet offering high connectivity had the limitation of high latency-a
significant slow down in speed between request and availability.
So the ideal network for storage has to transfer data across distances
pretty fast.
The
solution has come up in the form of fiber channel that can carry
up to 100Mbps for distances over 10Km. There are two forms of fiber
channel-the switched fiber channel and Fiber Channel Arbitrated
Loop (FC-AL). Switched fiber channel is based on the concept of
a fabric. The idea is that you connect into this fabric, which provides
connectivity between nodes that hook in. Today's fabrics consist
of a small number of very high-speed, low latency switches, but
can only handle a few dozen nodes connected to the fabric. An FC-AL
on the other hand, takes the loop shape. In this model, nodes are
connected via wires in a one way ring.
Implementation
architecture
The value additions from various vendors comes in the different
architectures they have for implementing SANs. Each vendor has a
proprietary architecture to support the SAN projects. Compaq has
its ENSA (Enterprise Network Storage Architecture) and IBM has Seascape.
"While SAN, NAS and DAS are the three most common ways of making
multi-user storage available to users, ENSA is an architecture and
a vision," asserts Khan. "ENSA envisages leveraging industry
standards to combine the benefits of distributed with the strengths
of centralized data management while achieving the highest levels
of performance and flexibility at the lowest total cost," he
adds.
SAN
vision for the future
A SAN, which is primarily a machine room technology because of limitations
of distance and bandwidth, is faced with the challenge of extending
and expanding itself across multiple sites such as a WAN. But bandwidth
limitations, inter-connect restrictions and prohibitive costs are
some of the factors which are stumbling blocks towards extending
SAN over WAN. Nevertheless, with advancements in technologies such
as fiber channel and asynchronous transfer mode (ATM), the future
vision of SAN is to actually offer global access to data across
an enterprise. A vision wherein an MNC can hook up its systems and
processes across the globe for information sharing and quick decision
making. And the last step in the road is to make the different SANs
across physical locations to be connected to each other.
An
open SAN
In addition to offering truly universal access to data-not just
across the range of computers, but across different geographical
locations-SAN's future direction is to offer total inter-operability
and open storage environment for the different storage components
across the network. For interoperability across standards and proprietary
technologies are still issues with SAN. The future direction is
to work closely with vendors and manufacturers of various components-hubs,
switches, routers, inter-connects, software and hardware-to arrive
at a standard open solution. In other words, to work towards an
open SAN.
While
SANs enable data sharing and data consolidation, the relevance of
the whole setup starts multi-vendor with applications running on
it across multi-locations. HP's 'apps-on-tap' is likely to emerge
as a break-through in this area. Under this, a widely adopted SAN
standard would make it possible for e-service providers of such
services as applications on demand (apps-on-tap) to retrieve information
at will from virtual data centers distributed over a wide geographic
region. This ability, enabled by intelligent SAN management software,
will allow application service providers to create mirrored storage
centers for data, ensuring that customers will always have access
to their vital information.