As companies rely more and more on e-commerce,
online transaction processing, and databases, the amount of information
that needs to be managed and stored can intimidate event he most
seasoned of network managers. While servers do a good job of storing
data, their capacity is limited, and they an become a bottleneck
if too many users try to access the same information. Instead,
most companies rely on peripheral storage devices such as RAID
disks, optical storage systems, and even tape libraries. These
storage devices are effective for backing up data online and storing
large amounts of information.
But as server farms increase in size,
and as companies rely more heavily on data-intensive applications
such as multimedia, the traditional storage model isn't quite
as useful. This is because access to these peripheral devices
can be slow and it might not always be possible for every user
to easily and transparently access each storage device.
Recently, a number
of vendors from all walks of the industry have been pushing a
concept called a storage area network (SAN). SANs provide more
options for network storage, including much faster access than
network attached storage (NAS) and the flexibility to create separate
networks to handle large volumes of data. This is the basic concept
of a NAS. NAS is straightforward in that disc arrays and other
storage devices connect through the network through a traditional
LAN interface such as ethernet. Storage devices attach to network
hubs much the same as servers would.
NAS makes storage resources
more readily available and helps alleviate the bottlenecks commonly
associated with access to storage devices. However, NAS does have
a few drawbacks. First, network bandwidth places throughput limitations
on the storage devices. Most NAS servers are placed on 10 or 100
meg/sec ethernet LANs, but even if a network is running at gigabit
speeds, most NAS vendors today only offer interfaces up to Fast
Ethernet. Another downside to NAS is the lack of cohesion among
storage devices. While disc arrays and tape drives are on the
LAN, managing the devices can prove challenging since they are
separate entities and are not logically tied together. NAS has
it's place as a viable storage architecture, but larger enterprises
require something a few steps beyond. Large enterprises that want
the ability to store and manage large amounts of information in
a high performance environment now have another option, the SAN.
In a SAN environment, storage devices
such as RAID arrays are connected to many kinds of servers via
a high-speed interconnection such as fibre channel. This setup
allows for any-to-any communication among all devices on the SAN.
It also provides alternative paths from server to storage device.
In other words, if a particular server is slow or completely unavailable,
another server on the SAN can provide access to the storage device.
A SAN also makes it possible to mirror data, making multiple copies
available. The high speed interconnection that links servers and
storage devices essentially creates a separate external network
that is connected to the LAN but acts as an independent network.
There are a number of advantages to SAN
and the separate environments they create within a network. SANs
allow for the addition of bandwidth without burdening the main
LAN. SANs also make it easier to conduct online backups without
users feeling a bandwidth pinch.
When more storage
is needed, additional drives do not need to be connected to a
specific server. Rather, they can simply be added to the storage
network and accessed from any point. Another reason SANs are making
big waves is that all the devices can be centrally managed. Instead
of managing the network on a per-device basis, storage can be
managed as a single entity, making it easier to deal with storage
networks that could potentially consist of dozens or even hundreds
of servers and devices.