It May No Longer Be NAS Versus SAN

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Networked storage will continue to see a truce, if not a nice cooperative
friendship, between storage area networks (SAN) and network-attached storage
(NAS) devices – two different methods of attaching storage and servers.

For the past several years, the trade press, however, has produced tons of
articles about the distinct differences between NAS devices and SANs. These
days trade press articles focus more on NAS devices and SANs being
complementary solutions for different storage needs and, and as a result of
this, starting to converse.

It all comes down to the bottom line – how and for what purpose does the
information, which that lives on the storage device, and the application,
which lives on the server, need to be move, managed, enhanced, and presented.

SANs emerged in the mid-1990s as a way to consolidate islands of
server-bound storage. The idea consisted of freeing the servers to do what
they do best – process data – while housing information in a central
location. Here the data can be managed, protected, and share. SANs also
reduce bulk of server-to-server data movement that has been clogging LANs for

SANs also optimize the speed of processing reads and writes for applications,
such as databases, and data warehousing, that require quick movement between
storage and server.

SANs have come about largely because of the Fibre Channel network
interconnection technology. A combination of industry-standard cabling
hardware and software protocols, Fibre Channel provides the capability to use
switches to interconnect multiple servers with multiple storage systems.
This technique enables an IT department to use familiar channel I/O-based
technology to build a fabric topology — one that connects many storage
elements with many computer systems. To this end, SANs can now provide
access to any storage system from any host or servers, thus making better use
of the storage assets and having them managed by fewer IT personnel.

NAS devices, on the other hand, use the maturity and ubiquity of IP-based
networks to provide access to stored information. While SANs provide channel
topologies to deliver large, block-level data to servers, NAS devices enable
many users to access individual files at the same time. NAS devices have
become ideal for serving Web pages to 1,000’s of workstations at the same
time. NAS devices have become popular in CAD/CAM environments where
engineers have to share design drawings. NAS devices appear like another
network drive a workstation can access.

To leverage the existing IP network for this purpose, NAS devices use
special file-serving protocols, such as NFS for Unix and CIFS for Windows NT.
These protocols enable the servers to communicate efficiently with a file

By managing the file system centrally, NAS devices enable multiple
workstations to access single files at the same time. The capability makes
NAS devices well suited for applications and environment requiring a great
deal of file sharing among multiple hosts or clients, even if they have
different operating systems.

Both NAS devices and SANs offer both advantages and disadvantages. On the
other hand, an enterprise storage infrastructure can require both NAS devices
and SANs. For example, an organization can use NAS devices for Web servers
and network-shared directories, and, at the same time, have SANs for
client/server and database applications. In some cases, the NAS file server
can be connected to the storage on a SAN.

Further, storage networking solutions that use multipath file-serving (MPFS)
software leverage the best of both SANs and NAS devices for use in a
traditional NAS application. Using MPFS software, large-volume NAS-based
data can be sent over a SAN channel to a host. This technique avoids the
performance decrease that may occur in an IP network when large files get

Although solutions like MPFS allow SANs and NAS devices to converge, an IT
department has to consider what’s the most productive way to use these two
network storage solutions – separately or combined.

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