you facing the challenge of preserving data? Here are a few
guidelines for choosing an appropriate Network Attached Storage
(NAS). by Mahesh Rathod & Suryakant Naik
is the most valuable resource for any organization. This makes
it imperative for IT managers to address the data storage
and management needs of an enterprise. Data needs to be stored
securely and made available round the clock.
Enterprise data storage started with server storage where
each server had its own built-in, dedicated storage. Then
came DAS (Direct Attached Storage), which utilizes a dedicated
storage server and contains a file system to manage storage.
These technologies however gave rise to performance issues
when many servers or hosts were accessing the same DAS.
NAS (Network Attached Storage) and SAN (Storage Area Network)
were mainly developed to address the limitations of these
NAS is based on mature technologies. It is platform and OS
independent and frees up processing power for key applications
running on the server, as it enables clients to access storage
across the network. NAS enables storage to be available independent
of server availability.
is based on open networking standards. There are two true
network standards for accessing remote data that have been
broadly implemented by virtually all Unix and Windows system
vendors. NFS (Network File System) is the de-facto standard
for Unix while CIFS (Common Internet File System) is the standard
for all flavors of the Windows operating system. As a result
of these broadly accepted standards for network data access,
storage devices that serve data directly over a network (called
Network Attached Storage or NAS servers) are far easier to
connect and manage than DAS devices.
Most NAS servers have their own file system, usually a thin
OS that performs the task of efficiently managing file services.
These thin OSs are mostly stripped down version of Unix, Linux
or Windows. NAS is the only form of storage that optimally
supports both NFS and CIFS network file system protocols for
sharing storage between Unix and Windows hosts. It is important
to note that about 75 percent of users today share data between
Unix and NT, making
these type of applications a key differentiator between DAS
In NAS, the client I/O requests are passed over a network
before arriving at the disk where the desired data resides.
Both the requested and the returned data pass through many
layers of software as the I/O makes its way from application
to disk and back again. It is important to remember that clients
send requests for remotely stored files over the network to
the NAS server. The NAS server returns the file to the client
after translating it into block addresses, retrieving the
data from disk and repackaging the data for transmission over
the network to the requesting client.
The selection of the right NAS solution can be based on the
following selection criteria:
Processors: Workgroup and lower end organization-level NAS
should have a single processor with a clock frequency ranging
from 300 MHz to 800 MHz for network processing, file and storage
processing. The main benefit of a single processor is the
low cost and drawback being the limited scalability in terms
of capacity and performance.
High-end enterprise class NAS should come with two or more
processors (minimum 800 MHz) based on whether they follow
symmetric multiprocessing architecture or functional multiprocessing
Memory: Workgroup or organization-level NAS should have minimum
of 128 MB memory, scalable to 512 MB depending on the number
of nodes on the network. Memory acts as Read/Write cache to
On the other hand, an enterprise-level NAS should have minimum
1 GB memory that is expandable to 3 GB. Disk data is cached
in this memory to accelerate client requests that access that
Network Interface: Workgroup NAS should support auto sensing
10/100 Ethernet with RJ-45 connector. Apart from the usual
10/100 Ethernet interface support, enterprise-level NAS server
should support Gigabit Ethernet with both fiber/copper connectivity.
NOS: Most NAS systems should support multiple operating environments,
some even allowing file sharing on the same device. For customers
this means flexibility, as a cross platform NAS not only provides
standardization of file services, but can also lead to cost
savings in staffing, training and deployment. Compatibility
list should include:
All flavors of Unix/Linux
Redundancy: There is no need for built-in redundancy
in workgroup NAS, since the cost factor becomes an issue.
On the other hand, enterprise-level NAS should at least provide
RAID level (0/1/5) protection for disk drives which utilizes
the same processor/memory for RAID operation. Since enterprise
NAS are robustly designed for 99.999 percent uptime, it should
provide redundancy from every prospective point like:
Power supply (N+1)
Drives (Hardware RAID with RAID 0/1/5/10) with Hot spare/
Hot swap features
Network Interface cards (Quad10 /100 / Dual Gigabit cards)
Performance: Performance for NAS is measured in terms
of Mbps. For workgroup NAS the performance should be at least
in the range of 30Mbps to 75Mbps. A NAS solution which offers
performance of 30Mbps can suffice the file serving needs of
25-30 nodes within a network.
Enterprise NAS performance is based on the following parameter:
I/O performance (from 10000 I/Ops to 75000 I/Ops)
Netbench (100 MB/sec to 160 MB/sec)
Sequential read write performance (120 MB/sec to 200 MB/sec).
Tape backup throughput ( 100 GB/ Hour to 200 GB/hour )
Alert system: NAS devices should have some type of
alert messaging system pertaining to drive failures, drive/file
system rebuilds, drives reaching capacity, unit reboot, unit
overheating and backup related messages, to administrator
/ user in the following manner:
LCD display on front panel
Event log option with browser management support
E-mail notification via SMTP
Event notification via SNMP
Here are some examples that might help you in deciding whether
a NAS solution is appropriate for your storage needs.
Unix and NT file sharing/storage consolidation: Since
NAS offers standardized, reliable and integrated file locking,
it is suitable in any application where business advantage
can be gained from sharing data between Unix and Windows and
from consolidation of data from numerous and distributed Unix
and Windows servers. For example a Windows client from purchase
department can access a Unix-based electronic document system
for engineering design in any engineering industry.
Technical/Analytical Application: NAS is ideal for
engineering application like Geosciences where a large file
or a group of files are simultaneously accessed by multiple
Geoscientists to perform data analysis on large database.
NAS is also well suited for decision support application like
data warehousing and data mining where companies collect large
amount of data for conducting statistical analyses to identify
Internet and Intranet applications: NAS devices can
be used as Web attached storage/Web cache in Internet applications
to offer significant improvement in system performance and
content availability. Internet applications include Web hosting,
e-mail, e-commerce and streaming media application.
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