Network attached storage is on the verge of widespread adoption as
suppliers boost performance and make systems easier to use.
Nicholas Enticknap finds out what it has to offer.
Network-attached storage (Nas) is a minority sport at the moment,
but one whose popularity is growing rapidly, driven by recent
improvements in the basic performance of the technology.
Suppliers have enhanced performance by building their products as
appliances - devices designed for a specific task. So Nas systems
now typically have their own purpose-built operating system that is
optimised for file sharing and is unable to run any other
application. An example is Network Appliance's Ontap, which
contains just 350,000 lines of code.
This approach makes the systems easier to use; boosts performance
by offloading a lot of the I/O traffic from the application server;
and aids storage management through the use of software
tools.
Nas was initially successful as a storage alternative for low-end
networks. It developed into a serious storage solution for a much
larger market with the emergence of storage area networks (Sans)
and Internet-based computing, which has created a much larger
requirement for file sharing.
Nas systems are very different from Sans, which are designed for
consolidating the storage used by multiple servers. Sans are
resource-sharing rather than data-sharing systems. Sans are
typically built using Fibre Channel technology, which is
significantly more expensive than Ethernet. They have their own set
of standards, which are still under development. And they are much
more complex, requiring skilled resources internally and usually
some external consultancy expertise as well.
On the plus side, Sans offer a much higher level of performance
than Nas systems because the Fibre Channel protocols were
specifically designed for storage systems, whereas the Ethernet
protocols used by Nas are general-purpose. Fibre Channel
connections have also traditionally been much faster than Ethernet
connections. Sans are much more scalable because they employ a
switched fabric, whereas Nas systems use point-to-point
connections.
Up until now, Sans have been installed by large enterprises with
the resources to manage the huge data storage requirement which
justifies the economies of scale a San provides. Nas systems have
also been installed by large companies for specific purposes where
file sharing is appropriate. For small and medium-sized
organisations, Sans have provided an entry point to networked
storage.
Thanks to two key technology advances, this picture is now
changing. First, Ethernet performance is now significantly faster
with the arrival of Gigabit Ethernet, and will soon get even
quicker with 10 Gigabit Ethernet. Second, a new protocol, ISCSI
(Internet Small Computer System Interface), designed for moving
storage data over Ethernet, is currently under development.
Taken together, these two factors are opening up the possibility of
Ethernet Sans. They will be attractive to small and medium-sized
organisations that have been put off by the cost and complexity of
Fibre Channel Sans.
Storage suppliers have moved on too. Up until 2000, the Nas market
was dominated by small specialist companies such as Auspex and
Network Appliance. The major storage suppliers were concentrating
on traditional direct-attached storage and on the newly emerging
Sans.
But the Nas companies have been very successful. Market leader
Network Appliance had sold more than 17,000 of its Nas filer
products. At the bottom end of the market more than 50,000 of
Quantum's small Snap Nas systems have been installed.
Analysts companies Gartner Dataquest and IDC put the total size of
the Nas market at between $1.5bn and $2bn (£1.04bn-£1.38bn) in
2000, and they are forecasting rapid market growth of about 60% a
year for at least the next five years, leading to a market worth
$6bn to $7bn by 2003.
With figures such as these it was not surprising that 2000 saw most
of the major server suppliers decide to enter the Nas market. Sun
introduced its Solaris-based Storedge N8000 in May 2000. Compaq
launched its NT-based Tasksmart N-Series two months later.
Hewlett-Packard joined in with a Nas version of the XP512. Dell
came into the market in September with the 705N, which was based on
a Quantum design, and then followed up with its own 735N product in
February 2001.
IBM dipped its toe in the water in September 2000 with an adapted
xSeries server, then entered the market seriously with the 300G Nas
bridge in February 2001 and two purpose-built Nas systems in
June.
EMC was an early entrant to the Nas market with its Celerra product
in 1996, which provides Nas functionality using the existing
Symmetrix disc subsystem. The company launched its first
purpose-built Nas system, the Clariion IP4700, in December
2000.
This flurry of new product releases changed the marketing
perspective. Up until this point, Nas and Sans had been promoted as
directly competing alternatives by both Nas suppliers and
traditional storage companies. But the industry has now adopted a
horses-for-courses approach - Nas is good for some things, Sans for
others. "Most organisations have a need for all the different
variants - direct-attached, Nas and San", says Garry Elliott,
Auspex's UK manager.
The recognition that Sans and Nas both have roles to play has also
contributed to a blurring of the boundary lines between them.
For example, several Nas systems now use Sans for storage rather
than their own dedicated discs. EMC's Celerra connects to a
back-end Symmetrix-based San, and can be split between Nas and San.
The IBM 300G is a similar product, also connecting IP network
clients to San storage. More recently, Hitachi Data Systems has
introduced Freedom Nas, which combines an HDS Thunder or Lightning
storage subsystem with a Nas server, and can, like Celerra, be
split between Nas and San.
Hewlett-Packard's Nas 8000, launched in March, can be either a
standalone Nas system with its own storage or a Nas "head"
(containing Nas functionality but no storage) connected to a San.
Auspex has gone down this route too, introducing a Nas controller
with San-based storage. "It will free up the 30% of storage on a
San that people don't know they've got", says Elliott.
Another approach is the "soft" Nas system, providing Nas
functionality for the user's existing storage hardware. This
approach has been pioneered by Novell with Netdevice, which was
launched in July 2001. The company says Netdevice will plug into
any network and allows the use of any storage hardware. It is
shipped as an integral part of Netware 6 but can also be bought
separately. The product is selling well. "Where small offices use
shared storage, so use of the Internet is impractical, Nas is
ideal," explains Brian Green, director of Novell's Network
Management Group.
Traditional Nas systems are also evolving. As in other areas of the
storage market, capacities and performance are improving all the
time. Performance has also been improved by the arrival of Gigabit
Ethernet and of TCP/IP offload engines. More significantly, Nas
systems are acquiring enterprise-class characteristics they did not
previously have.
The Dell 735N has snapshot and mirroring capabilities. Network
Appliance has also been adding mirroring software. In addition, it
has improved the system's high-availability characteristics. EMC's
Clariion IP4700 was designed with high availability in mind from
the start, and has no single point of failure. IBM's Nas marketing
manager Roger Messenger says, "We emphasise data protection as a
major feature of the Nas 200 and 300."
There is now a move towards making Nas systems suitable for sharing
databases as well as files. A major feature here is the development
of the new file-sharing protocol Dafs (Direct Access File System).
Network Appliance's Northern Europe SE director Stuart Gilks says,
"Dafs will offer benefits especially in high-transaction,
high-performance environments."
Dafs was announced June 2000, and is being developed by the Dafs
Collaborative, an industry consortium of 80 members. Demonstrations
of IBM DB2 and Oracle 9i applications running over Dafs took place
in June 2001. The final specification was completed in October and
is now under consideration by the Internet Engineering Task Force.
Products implementing the protocol are likely to arrive soon,
probably in the second half of this year.
So who should use Nas? Encouragingly, the range of applications is
wide. Today it remains an option for specific enterprise tasks -
"Where there is unstructured data that needs to be shared in file
mode, with a requirement to share between many end-users," as EMC's
Nas SE manager Mike Bradley puts it. Here the question is whether
to use a dedicated standalone system or build in Nas functionality
as an integral part of a storage network.
But the main application has to be consolidation. Look at Nas if
you are in a small to medium-sized company that does not want the
complexity of Fibre Channel Sans but does want the benefits of
consolidation, whether in a file sharing context or not.
What is network-attached storage?
Network-attached
storage (Nas) is a specialised form of networked storage that was
initially designed for sharing files between graphics workstations.
This historical background still affects the design of Nas systems
today.
Nas is used for file sharing between computers running different
operating systems and file structures. All Nas systems support the
two most common file sharing protocols, NFS (Network File System)
and Cifs (Common Internet File System). So Nas systems can share
data between different kinds of Unix systems and between Unix and
Windows systems.
Nas was the first type of storage system to offer genuine data
sharing between different computers, as opposed to simply disc
sharing.
Nas systems are attached to Ethernet local area networks, so
installing Nas requires no new technical equipment or changes to
servers - it is plug-and-play. Most Nas systems can be up and
running within 30 minutes of leaving their boxes (or less).
Nas also requires no new expertise on behalf of technology staff -
all the standards governing Nas systems are well-established and
all the technologies are familiar.