isn't enough to simply add disks to your servers and store
data. How do you archive, manage, protect, and share it with
other departments and users in your organization? by Soutiman
disk after disk to your enterprise servers is like putting
all your eggs into one basket. A number of troublesome issues
will soon crop up. What's the use of having data lying around
on servers if it can't be easily accessed? So you need to
devise a mechanism by which all the company's locations are
able to access the valuable data. Then take care of another
thing make sure you don't lose all the data in a disaster.
The acquisition of storage needs to be more than just a disk
or tape purchase. Your network should graduate to accommodate
the storage architecture and function as a whole.
Part of laying a foundation to a storage solution is to understand
the kind of OS (Operating System) environment and the technical
architecture that defines how storage is connected to the
servers which execute the various enterprise applications.
solutions significantly depend on OS environments. The various
flavors of Unix and Windows NT/2000 represent the open systems
area. There is a lot of diversity in these systems and many
hardware and software solutions may not operate on all of
them. The current versions of NetWare, Windows, and all Unix
variants have good support for storage integration. IBM dominates
the mainframe world with its MVS, OS/390, and z/OS and SSA
(Serial Storage Architecture) hard disks. Any solution for
such an environment must integrate fully into the IBM platform.
Lately, IBM has developed an architecture that integrates
with other open environments as well.
Avijit Basu, Marketing Manager, NSSO, at HP India says, "The
pre-open system environment or the mainframe era had old,
expensive, and proprietary storage technology. It originated
at a time when an open system environment was not as demanding
in capacity, performance and reliability as it is today."
Balasubramanian, Head, Storage Division, Sun Microsystems
adds to the above, "In a strategy to control the market
some vendors offered costly proprietary solutions. Some of
these solutions even have reduced functionalities. But this
strategy has changed now that more users demand open network
(Direct Attached Storage) is commonly used for storing data.
But it is limited because it does not allow an organization
to share data easily. It is not an enterprise network storage
architecture in a true sense. It is also inflexible and has
short-term cost and technology benefits. NAS (Network Attached
Storage) and SAN (Storage Area Network) have evolved as more
reliable enterprise network storage architectures. Let's look
at all three of them in detail.
'DAS' the way most like it
is the most common form of storage used by companies. In this
set up, most computer storage devices like disk drives or
JBODs (Just a Bunch of Disks), tape devices, and RAID systems
are directly attached to a client computer. They use various
adapters and standardized software protocols like SCSI (Small
Computer Systems Interface) and FC (Fiber Channel.)
In DAS, I/O (Input/Output) is done in blocks from the server
to the storage. This type of storage attachment has set the
standard for performance and utilization by the server. With
DAS, performance is typically characterized by response time
for access to data and by bandwidth for aggregate transfer
rate of data.
On the flip side, DAS has limited flexibility and does not
allow you to scale outward easily. A company's network will
typically continue to grow while data on the various DASs
will remain scattered at different locations of the network.
This will not allow all the users in the network to access
and share the data. Management becomes a hellish task with
so many disparate 'islands' of information all over. Data
security and protection is equally difficult as no form of
centralized control can be established.
It's no secret that companies that are serious about their
data cannot rely on DAS as an effective storage strategy.
It has too many limitations. And IDC estimates that storage
management costs can be reduced by 40 percent and IT administrators
can manage 750 percent more storage capacity by moving out
of the traditional DAS.
However in a SOHO environment with very few users, a DAS can
handle the storage needs fairly well.
is a specialized file server that can be plugged into the
network (LAN) just like a network printer, hence the name
'network-attached'. It provides file-level access to data
and uses standardized protocols like NFS (Network File System-Unix-based),
CIFS (Common Internet File System-Windows-based), and TCP/IP
to communicate. One of the many beautiful features of a NAS
is that it can serve both Unix and Windows users seamlessly
and share the same data between the different architectures.
It is ideal for mid-sized and not-so-large companies who have
a fairly large volume of data.
With a NAS, storage does not become an integral part of the
server. It has a storage-centric design where the server still
handles all the processing of data but the NAS device delivers
the data to the user. If you have an overflowing hard disk
on your main server, a NAS device can allow you to stretch
and offer breathing room. You can move archives or completed
projects from the main server to the NAS and still allow users
in the network to access it. Data storage, security, and backup
management can also be centralized.
systems can access data from a NAS over a network via a file
'redirector' that changes the access to a file from the native
file system (on the originating computer system) to a network
operation using TCP. The remote NAS device runs software that
allows the file system to support an individual client access.
The file system on the NAS server determines the location
of the data requested by the application client whether it
is in its cache or on the storage.
NAS causes overhead for using the LAN since it rides on the
TCP/IP protocol stack and consumes processing power. It may
bring latency into the network when another processing element
is placed in the I/O access path.
SAN is a high-speed dedicated storage network or subnetwork
which can integrate RAID arrays, tape backups, CD-ROM libraries,
and JBODs. The SAN network allows data transfers between computers
and disks at the same high peripheral channel speed, as if
it is directly attached. It is ideal for large companies that
have networks across large geographical areas and medium companies
who expect quick growth. SANs are used by industries like
petroleum, banking & financial institutions, and retail
deployments are largely driven by the use of the FC standard
as a common interface. FC makes use of a circuit/packet switched
topology capable of providing multiple simultaneous point-to-point
connections between devices. It offers advantages like good
connectivity over large distances and scalability. The SAN
advent is driven by new requirements of applications like
data warehousing, data mining, and OLTP (On Line Transaction
Processing) which need high bandwidth and tolerate zero latency.
The FC interconnection protocol allows data transmission speeds
up to 1 GBps, which is much faster than traditional SCSI-based
PC and server devices which have a maximum speed of 160 MBps.
SANs see storage as separate from a server like NAS. But unlike
NAS, the SAN architecture involves an independent network
or subnetwork. It provides its own network to storage and
offloads primary network from all storage related I/O and
backups. With a SAN, servers are not directly involved in
the storage process. They simply monitor it. And by removing
I/O from the servers and the LAN/WAN, you free up bandwidth
for applications. This allows enhanced network performance
and removes traditional bottlenecks. With the use of a SAN
switch you can permit concurrent traffic between all servers
of the network and share all the storage devices.
support disk mirroring, backup and restore, archival and retrieval
of archived data, data migration from one storage device to
another, and sharing of data among different servers in a
network. SANs can incorporate subnetworks with NAS systems.
FC is without any question the backbone of a SAN architecture
but SCSI can be used as the interface to link storage devices
to the SAN backbone. This is because FC supports simultaneous
transfer of different protocols. SANs also support ESCON (IBM's
optical fiber interface).
Instead of putting the storage directly on the network, the
SAN concept puts a network in between the storage subsystems
and the server. This means that a SAN actually adds network
latency to the DAS storage model. SAN standards are still
in the formative stage and vendors like EMC, Compaq, and HP
have announced proprietary standards. This collection of proprietary
architectures may create roadblocks to successful NAS and
SAN integration and data sharing between heterogeneous platforms.
The big question
Since there are various storage topologies available, the
big question is, how do you decide which is the best for your
company? A good way to begin is by studying the differences
between DAS, NAS, and SAN. (see table DAS, NAS, and SAN-A
DAS is appropriate for very low-end applications like home
office environments and with portable computers. It can be
difficult and expensive to add networking to the storage architecture.
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 NT hosts. Since it offers standardized,
reliable, and integrated file locking, NAS servers are suitable
for many applications where business advantage can be gained
from sharing data between Unix and Windows NT clients. It
is important to note that file sharing applications provide
not only business benefits to non-IT departments but also
offer a major infrastructure benefit to the IT department
like increased storage utilization.
A SAN may not be a good idea if your network has many OSs
and platforms. And installation is comparatively difficult.
But its advantages are numerous. It easily supports multiple
user access without much overhead. The architecture is optimized
for high usage, multiple access, and transfer of large files.
Storage capacity can scale upward easily using FC switches
and storage devices without adding significant costs. Redundant
hardware and software components provide high availability
and the system can be configured so that there is no single
point failure. Such an architecture makes it an ideal choice
for large enterprises or enterprises who foresee positive
business growth. It can also support a feature called server-less
Owais Khan, Business Manager, Enterprise Storage at Compaq
says, "In order to help decide which storage architecture
to use, the IT Head needs to make a preliminary review of
its current IT infrastructure, data storage capacity, and
volume generation. He/she should then map the required storage
capacity against the business growth plan. The organization
must also consider disaster recovery solutions. Enterprise-wide
backup solutions with built-in centralized management functionality
need to be deployed. It is also important to consider the
levels of service and support that the vendor can provide.
Only when certain key checklist criteria have been assessed
does the IT Head decide which solution, whether NAS or SAN
is more appropriate for the enterprise."
Migration: Turning NAS-ty
users in India use DAS for storage. But as network data rates
slowly exceed the capacity and speed of DAS systems, SANs
and NAS will certainly present itself as the next option of
storage architecture," feels Ramesh Ramnath, Manager,
Systems Engineering at Cisco.
It isn't rocket science to migrate to a NAS environment from
your legacy server-based storage architecture or DAS architecture.
Anand Padmanabhan, Head, Enterprise Products Divisions at
Wipro Infotech says, "You can move the existing data
into a NAS box and simply plug-it on to the network. This
is in simple terms migrating to a NAS."
Sam Thomas, Senior Marketing Manager (Products), Acer India
says most NAS solutions support multiple protocols like NFS,
CIFS, and HTTP. "So an organization can migrate its data
that resides on heterogeneous server platforms to a common
NAS server. Servers can then transparently access the data
residing on the NAS devices."
Unifying NAS and SAN
spite of vendor hype and claims to offer integrated NAS and
SAN architectures, it is not possible to deploy an optimally
integrated NAS and SAN architecture today. There are significant
technical challenges that emerge when you try to integrate
block-oriented SAN and file-oriented NAS storage access methods.
Blocks are physical data concepts that refer to the organization
of data on a disk drive in terms of sectors and tracks. Files
are logical data representations which are understood only
by a file system and are made of multiple blocks, sectors
A disk drive has no knowledge of files. The translation between
the logical file data and the physical organization of this
data into blocks on a disk drive is the job of the file system.
File systems are usually embedded in a client or server's
OS (local file system) but remote file systems over a network
like NFS or CIFS have become standard for offloading block
retrieval processing using redirector software.
order to integrate NAS into a SAN fabric the challenge is
to connect the NAS storage to a fiber channel switch while
retaining its data integrity. This opens access to the NAS
storage by all authorized servers within the SAN fabric. This
also allows the NAS storage to enjoy the benefits of centralized
backup to a tape library configured within the SAN fabric,"
says Savio Monteiro, Country Sales Manager, Channels of Vertias.
A great deal of NAS storage is SCSI-based, with internal drive
and channel architecture that uses SCSI or the latest Ultra3
SCSI. Typically, a SCSI NAS will interface with a 10/100 Ethernet
LAN and allow multiple Ethernet ports. Since SCSI NAS cannot
directly interface to a fiber switch, the key is to insert
an external router that accommodates SCSI input and provides
achieve efficient backup and recovery in an enterprise, you
should take a consolidated information infrastructure approach.
In a traditional distributed enterprise with decentralized
storage, each platform has its own storage and backup process.
EMC's Country Manager, T. Srinivasan says, "In order
to achieve zero downtime, you have to centralize the information
through a networked storage infrastructure. This allows the
information to be centrally protected, shared, and managed.
The storage software will then enable business continuance
on top of the networked storage layer." You can use the
usual backup devices like various tape and disk drives.
An enterprise can lose data due to a number of reasons like
human errors, disk failure, hardware and software malfunction,
and natural disasters. There are a variety of hardware and
software tools available to perform efficient backup and recovery.
Some examples are tape drives, tape autoloaders, tape libraries,
and software like Legato Networker, Veritas NetBackup, and
R. Prabhakar, Associate VP, Managed Services at Bangalore
Labs says, "Traditional means of disaster recovery were
to make backups on tapes and storing copies at a remote location.
Today there are various options available depending on the
restoration time that you expect from the disaster system.
Typical restoration times with backups range from an hour
or more depending on your data size and backup policy. If
you need restoration times in minutes, you need to use disks
instead of tapes. NAS and SAN systems allow you to create
snapshots of data that can be replicated to remote systems
over a traditional TCP/IP network or through dedicated fiber
Whatever may be the choice of storage, most IT Heads need
to realize that even in today's tough economy if you create
a comprehensive storage strategy, it will translate into competitive
advantage and significant financial gain.
Das Gupta can be reached at firstname.lastname@example.org