Storage area networks offer the flexibility to mix and match
storage system suppliers, as well as allowing storage to be
concentrated and consolidated. Liz Warren explains how Sans could
solve your problems
The growth in e-commerce and other Web-based activities, together
with data warehousing and increased use of multimedia data in
applications such as digital imaging, has led to a phenomenal
growth in storage requirements.
Strategic Research, a market research company which specialises
in tracking storage trends, estimates that storage demands are
doubling roughly every two years. On top of that, the move towards
customer-focused marketing and supply chain integration means that
different applications often need access to the same data at the
same time.
The sheer volume of this data - and the fact that it
increasingly needs to be available around the clock to support 24x7
operations such as Internet sites - presents a new set of
management challenges to IT directors. Storage area networks (Sans)
aim to address these issues.
Almost all storage today is "bus attached" - that is to say it
is connected directly to a particular server using SCSI or IDE
(integrated drive electronics). Network-attached storage (Nas) and
Sans both evolved as a way of consolidating storage and bringing it
out from behind particular servers whose capabilities and loading
can limit access to the data. The difference between Nas and a San
lies in how that storage is made available to users.
San vs Nas
Nas attaches a disc array directly to the main communications
network, which links clients to servers via a processor running an
operating system which deals with file I/O protocols such as NFS
(network file system).
By contrast, a San comprises a dedicated high-speed network
sitting behind the servers and connecting multiple storage devices
to the back ends of multiple servers. It uses a storage protocol,
such as SCSI or the newer fibre channel standard, to transfer data.
A San also incorporates a management layer which organises the
transfer of data, allows storage devices to be controlled and
handles tasks such as back-up and replication.
If you believe San suppliers' marketing, you might think it
equals fibre channel. However, Michael Peterson, president of
Strategic Research, says Sans are not a new idea. Those based on a
network storage interface called Escon have been connecting
mainframes to multiple storage systems for years, he explains. What
is new is that San architectures are now being applied to
distributed systems such as NT and Unix.
According to Andrew Rowney, sales and marketing director at
Storage Area Networks, fibre channel has become associated with
Sans partly because, running at 100mbps, it initially offered a
considerable performance advantage over SCSI running at 40mbps.
However, Rowney suggests it is perfectly possible to create a San
using an established storage network protocol like SCSI, especially
given the development of the new backward-compatible SCSI standards
running at 80mbps and 160mbps.
Whichever protocol you use, San suppliers claim the architecture
offers a number of benefits. First, consolidating your storage in
one place should help you to cut the cost of managing it. Peter
Coleman, technical manager at San hardware supplier Gadzoox, points
out that IDC estimates that a single technician can look after
about 100Gbytes of server storage, with the result that management
costs eat up half the storage budget. When storage is centralised,
the same person can manage 750Mbytes of storage, reducing the
management overhead to just 15% of the overall cost.
On top of that, consolidating your storage devices allows you to
deploy them more flexibly - re-allocating spare capacity on one
system to another server, for example. This should result in a
better return on your investment in existing storage devices and
may help you avoid unnecessary expenditure.
Capital expenditure
Although the capital expenditure associated with deploying Sans
can be quite high, Coleman believes these costs can be recouped
relatively easily. However, Gregg Ormsbee, product development
director at Tandberg Data, warns that current San solutions have
only begun to scratch the surface in terms of consolidating
storage.
At present, each application is still likely to have its own
dedicated data store and discs. Ormsbee expects to see increasing
synchronisation of data between applications, leading eventually to
the development of a single data store containing a superset of all
the data in the organisation, together with metadata describing how
it should be used by different applications.
One of the drawbacks of consolidating your storage devices in
one place is that it could make your data more vulnerable. But it
also makes it much easier to replicate that data, and one of the
most prominent features of the new fibre channel protocol is its
ability to link devices across a distance of 10km, allowing remote
vaulting of data and high-speed transfer of data between sites.
Rowney points out that to take advantage of this feature you
need access to a fibre channel link between the two sites. "Even
today, you can't buy fibre channel services from [telecoms and
Internet service providers], and most companies don't have the
opportunity to lay their own cable," he says.
However, carriers do offer asynchronous transfer mode (ATM)
backbones which can provide high-speed links over much greater
distances than fibre channel. Not surprisingly, Rowney's firm has
developed a product which allows Sans to be connected through ATM
links.
Apart from helping IT managers to protect their data through
improved back-up, San technologies lend themselves particularly
well to use with other high-availability techniques such as
clustering. Coleman points out that operating systems such as
Windows 2000 and Netware 5 have been specifically designed to offer
clustering of standard Intel platforms connected to Sans. Multiple
pathways between storage media and servers in a well-constructed
San can also help to ensure high availability of data.
Significant improvements
According to Coleman, another benefit of attaching all your
storage devices to a dedicated network is that it offloads traffic
from the Lan. As a result, users may see significant improvements
in the performance of applications, given that up to 30% of all Lan
traffic is due to back-up. This will become increasingly important
as 24x7 operations such as e-commerce become more widespread and
overnight back-up windows disappear. Back-up via a San will also
minimise the impact on users when a system failure means data needs
to be restored during the normal working day.
Coleman says the ability to shift traffic off the Lan makes Sans
particularly suitedto applications which involve moving largefiles
around - such as video streaming or pre-press work in the
publishing industry - because storage protocols are designed to
offer much higher sustained data rates than Lan protocols.
However, implementing a San to achieve these benefits is still
far from straightforward. According to Chris Boorman, Euro-pean
marketing director at storage software specialist Veritas, the
quality of San offerings can vary between suppliers, and even
within a supplier's turnkey solution. He believes that good San
solutions will only be achieved by carefully selecting and
integrating best-of-breed products for each of the technologies
which make up a San - San hubs and switches, host bus adapters
which connect servers to the San, management software and the
storage devices themselves.
Ormsbee says unified standards for San, allowing plug-and-play
interoperability, are still six months away. He and Coleman agree
that integration skills will be essential to the success of San
implementations. "You need an integrator which can bring together
best-of-breed products to meet your business needs, rather than
going to a single supplier who might be able to offer a turnkey
solution but not one that is best for your business," Coleman
argues.
Rowney warns that such skills may be in short supply in the
immediate future as storage suppliers - which have not been noted
for their consultancy and integration skills in the past - struggle
to develop channel partners with the right expertise.
IT managers will find that storage management software is only
just beginning to incorporate some of the features needed to
implement Sans supporting more than a limited number of servers -
controlling which servers have access to which data, for example.
Early adopters of Sans should prepare themselves for a rocky road
before they reap the benefits.
San suppliers
Associations
Fibre Channel Association - http://www.fibrechannel.com -
01635-874330
Storage Network Industry Association - http://www.snia.org -
001-650 949 6750
Suppliers
Brocade Communications - http://www.brocade.com -
01344-750190
Computer Associates - http://www.cai.com/arcserveit -
01753-577733
Dot Hill Systems -
http://www.dothill.com/products/sannet/san_net.htm - 020-8874
5252
Exabyte - http://www.exabyte.com - 0800-966172
Gadzoox - http://www.gadzoox.com - 0118-988 0262
IBM Numa-Q - http://www.sequent.com - 01932-851111
Legato Systems - http://www.legato.com - 01628-511811
M4 Data - http://www.m4data.com - 01252-864600
Mylex Corporation - http://www.mylex.com - 01256-334000
Network Appliance - http://www.netapp.com/products/filer -
0771-445 6233 Overland Data - http://www.overlanddata.com -
0118-989 1891
Storage Area Networks - http://www.san.com - 01223-566111
StorageTek - http://www.storagetek.com - 01483-737333
Tandberg Data - http://www.tandberg.com - 01582-769071
Tivoli Systems -
http://www.tivoli.com/products/index/storage_mgr/ -
01753-780000
Veritas - http://www.veritas.com - 01932-876876
Before you buy
- Decide which data and applications warrant the cost and
complexity of a San
- Find a partner with integration skills who is willing to take
responsibility for delivering an end-to-end solution
- Look for a solution which is scalable and can incorporate
legacy storage devices
- Before buying, ask for the particular combination of products
you want to use to be tested in an interoperability lab
- Make sure you understand which protocols your supplier is using
and how they plan to migrate to unified industry standards once
they are agreed
- Check support for management activities such as dynamic
re-allocation of resources
Case study: Nationwide Building Society
Nationwide, the UK's largest building society, has pursued a
policy of centralising its data for a number of years. However, the
advent of Windows NT-based systems, which typically involve
multiple servers, meant that traditional connection protocols could
not keep up with the number of servers which now need to be
connected to central data stores - which are themselves growing
larger.
"You can now get devices with seven or eight terabytes in a box
which can support a hundred servers, but you can't connect that
many via SCSI," explains Martin Conway, a technical consultant at
the building society.
On top of that, Nationwide had a number of other goals:
connecting servers to storage over greater distances; implementing
dual-port connections to improve resilience and load balancing;
improving performance in its data handling activities and achieving
greater flexibility in using and sharing devices such as tape
drives.
The building society quickly realised that San technology
provided an answer to all these challenges. However, it decided to
implement a San only when suitable management software became
available. "The physical technology has been there for some time,
but not the software needed from a security perspective to allow us
to control which servers see which discs," Conway explains.
Nationwide now has a San based on StorageTek's Access Hub, which
is connected to disc storage from EMC as well as products from
Digital, Compaq and Emulex. Connection to tape storage is currently
being investigated. Nationwide chose StorageTek because of its long
relationship with the supplier,and StorageTek's ability to provide
a suitable device backed up by high levels of implementation
support,which sawthe supplier underwrite the provision of an
end-to-end solution.
The key decision was whether to go for hub or switch technology.
"Switch technology offers the advantage of any-to-any connectivity,
but it's costly," Conway says. "In the NT space, you need a lot of
ports, so the cost-per-port becomes an issue. A solution based on
intelligent hubs - where you can change loop configurations on the
fly - offered us the best compromise of cost and functionality.
However, switching suppliers are driving their costs down and later
this year we will be looking at whether to intro-duce switches
between the storagemedia andthe hubs."
Case study: BSkyB
The award-winning 3D and special-effects department at satellite
broadcaster BSkyB is responsible for producing animations and
promotional segments for channels including Sky One and Sky News. A
minute of video takes up 1.5Gbytes, handling and sharing data is a
major issue for the department, but a San installed last year has
enhanced productivity by making it easier for users to share data.
Because it is based on a Raid array, the San has also increased the
security of the data.
Previously, data was stored on individual workstations connected
via Ethernet. Dave Sedgwick, BSkyB's visual effects supervisor,
explains, "Before the San installation, if someone needed to work
on a different workstation, it would take longer to move the data
than it would to complete the project".
The new set-up, which was implemented by storage integration
specialist Sagitta, links seven NT workstations to a 144Gbyte Raid
array using a Gadzoox Gibraltar fibre channel-managed hub. One of
the key reasons why the company chose Gadzoox for the project was
because it has a strong reputation in the storage community for
this size of San installation. BSkyB did consider using gigabit
Ethernet rather than a San but decided it was not mature enough to
meet its needs.
Installing the San was not completely straightforward. According
to Sedgwick, there were a number of interoperability issues to be
resolved during the implementation, particularly when connecting
Silicon Graphics workstations. And there are a few bottlenecks
which still need to be addressed.
If these issues can be resolved satisfactorily, BSkyB is
considering extending the San to support more storage and up to 80
end-users.