While
storage area networks (SAN) provide
substantial performance and utilization benefits for a data
center, not every organization can justify the cost and
complexity involved. In many cases, storage can be added to the
network using
network attached storage (NAS) devices --
dedicated disk-based storage devices that attach to the user
local area network (LAN) through an ordinary
network connection. NAS devices can be expanded with additional
disks, and new NAS appliances can be added
as needed to facilitate significant amounts of network storage.
Not all NAS devices include their own storage. NAS
gateways basically provide NAS functionality
to externally connected storage; most often through a
Fibre Channel (FC) connection. Thus, a NAS
gateway can connect to a storage array or SAN storage.
NAS management software tools will need to be selected to
identify available storage, handle
backup and restore tasks, support
replication and tackle a variety of other
data protection tasks. Most NAS devices include vendor-specific
management tools, but there are some generic tools intended to
provide
heterogeneous NAS platform support. Aside
from considering the obvious issues of pricing, management and
support, here are some other important points to keep in mind
during any NAS purchase.
@29473 Determine the underlying need for NAS. Before
selecting a storage platform, consider the applications that will
be using the storage -- storage should accommodate the
applications, not vice versa. Some file-based application data,
such as images and Word documents, are better suited to NAS
platforms. Block-based applications, like databases, may achieve
better performance through SAN storage. It is also possible to mix
architectures using a NAS gateway to allow file-based access to SAN
storage.
Consider storage needs over the long haul. NAS may be
easy to implement and expand, but it can become difficult to manage
as deployments proliferate. Before making a NAS investment,
consider the changing patterns of storage allocation and use in
your enterprise. For example, several
terabytes (TB) of NAS might meet immediate
needs, but adding several TB per year across numerous NAS
devices might soon become impossible to administer. In those
situations, an investment in SAN might be more appealing or opt
for a large-capacity NAS up front to consolidate storage systems
early on. Also, explore potential upgrade paths to learn how
future updates will impact storage performance and total cost.
For example, more expensive NAS platforms may be more
cost-effective over time if they are easier and cheaper to
upgrade.
Consider different modes of implementation. Generally
speaking, there are three ways to implement NAS -- use a dedicated
NAS system (appliance) with its own local storage; use a NAS head
or gateway to access external storage on an array or SAN; or some
combination of both approaches. Dedicated NAS appliances are often
preferred when simplicity and ease of deployment is most important
and little scalability is needed. NAS gateways provide access to
considerably more potential storage, but can be more complex to
manage due to the provisioning and security implications of SAN
storage. Weigh the tradeoffs carefully before choosing an
approach.
Consider product utilization and value. Industry experts
note that NAS selection criteria should extend beyond getting the
most storage for the minimum cost. The problem is that many NAS
features have little tangible value other than differentiating
vendors. In addition to the cost/capacity tradeoff, take an honest
look at the features and functionality that you will actually use.
For example, it may be worth spending a little more up front for
key features that improve performance or ease management; as long
as the real benefits outweigh the costs. Conversely, exotic
features (e.g. remote snapshots) may look appealing on paper, but
they're not worth the added price if you never intend to use them.
Weigh the impact of related factors like reliability, ease-of-use,
vendor support and interoperability.
Consider the management overhead. NAS appliances and
gateways will need to be managed using software tools. Management
overhead will typically increase as NAS storage expands and
proliferates across multiple devices. Over time, NAS management
overhead can become unwieldy -- working against the ease and
simplicity that NAS is known for. Make sure that any NAS management
tools support the NAS hardware deployed across your infrastructure.
Try to avoid multiple tools if possible. NAS appliances with
internal storage offer convenience, but NAS gateways are sometimes
selected when heavy storage demands are expected "outside of the
box." Difficult management can sometimes be eased by consolidating
multiple NAS devices into a single NAS platform or shifting NAS
storage to the SAN using a NAS gateway. Virtualization can also be
applied to achieve a higher level of intelligence, ease management
and improve utilization of the physical storage.
Evaluate the performance of any potential NAS device. LAN
connectivity can be a potential bottleneck with NAS devices, and
storage performance can suffer with heavy network traffic or
storage I/O requests. It's important to test the performance of
your applications running on a prospective NAS device. Ensure that
the NAS device can meet the I/O and latency demands of the
applications. When high performance and availability are needed,
select a NAS system with multiple high-speed LAN ports that support
aggregation and failover. It's also worth examining performance
against scalability to ensure that the NAS product will continue to
perform adequately as it scales up.
Define any new or different skill sets that are required.
Although NAS devices offer a lot of similarities, there are also
subtle, and sometimes not so subtle, differences between models and
manufacturers. For example, some NAS boxes run common operating
systems (OS), such as Windows, while others may utilize a
manufacturer-specific OS. When studying the requirements of a
prospective purchase, you should identify areas where IT staff may
need additional or supplemental training to install, configure and
support the NAS box. New skill sets often cost money, raising the
total cost of ownership (TCO) of a prospective purchase. In many
cases, lab testing prior to a purchase can familiarize staff with
basic NAS operations, allowing them to ask more informed and
pointed questions during manufacturer training sessions.
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