the volume of data generated in business grows, it becomes
increasingly difficult to manage data and storage subsystems.
A storage architecture is the solution, but how do you
choose the right one for your enterprise?
may be a prized business asset, but what's the use of
having it digitized and stored away if one can't access
it when it's needed most? Organizations store data on
various storage subsystems scattered across the enterprise.
So locating a specific piece of information may be a
tedious and time-consuming process. Managing multiple
storage subsystems can be a harrowing task for network
administrators. Another problem is the growth in the
volume of data that's generated as business expands.
The solution to all this is a proper storage architecture
that provides for scalable systems, integration and
management of storage subsystems. The solution should
also offer data security, protection and recovery.
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 that execute the different
Besides choosing a suitable storage
architecture and implementing the appropriate
solutions, an IT manager must also consider data
protection and recovery. For this there are backup/restore
strategies and solutions.
To achieve efficient backup and recovery in an
enterprise, one should take a consolidated information
infrastructure approach. In a traditional distributed
enterprise with decentralized storage, each platform
has its own storage and backup process. To achieve
zero downtime, the information must be centralized
through a networked storage infrastructure. This
allows the information to be centrally protected,
shared, and managed.
storage software will then enable business continuance
on top of the networked storage layer. You can
use the usual backup solutions like various tape
media and disk drives.
In a server-less backup architecture, the tape
device is delegated the role of a system coordinator.
In a traditional LAN environment multiple clients
or servers get backed up to one server that has
the tape automation subsystem attached. Backup
tapes are duplicated at each server or over a
LAN using products like Legato NetWorker or Veritas
NetBackup. This technique provides a central point
of control for the backup software, but has the
disadvantage of requiring all data to be passed
across a relatively slow LAN to the server performing
A SAN solution eliminates the LAN bottleneck and
provides direct backup from multiple servers to
the tape automation subsystems. This LAN-free
backup technique provides multiple paths into
the tape automation systems typically through
a FC hub or switch. The SAN architecture for tape
backup also eliminates the need to pass the data
from the disk arrays through a server.
With server-less backup, the server issues the
backup commands (control path), but the data path
goes directly from the disk subsystem to the tape
automation subsystem. This technique frees up
cycles on the server to do productive processing
and simplifies the movement of data.
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 CA ArcServe.
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.
Media and backup devices
There are various types of storage
media that an enterprise can use for primary storage
The most common storage media in use today. The
data is stored on magnetic or optical disks. Magnetic
disks have storage capacity upto 100 GB and optical
disks even more. Many factors affect the performance
of a disk drive like data transfer speed, latency,
access time, and revolution speed.
Hard disks are either IDE ((Integrated Drive Electronics)
or SCSI. The advantage of IDE is its lower cost.
And the advantage of SCSI is that up to seven
or more devices can be attached to the same controller
board. SCSI drives are typically used in high-end
servers and storage networks.
A good choice for creating backup and can be an
essential ingredient of a disaster recovery solution.
It can be stored in libraries for easy access
and management. Currently tape cartridges can
support upto 10 GB storage. Tape drives are available
in formats like DLT (Digital Linear Tape), LTO
(Linear Tape Open), Ultrium (A high-end LTO format),
DAT (Digital Audio Tape), QIC, and Travan formats.
This media provides a high capacity solution.
You can share, store, backup, and transport large
multimedia and data files. DVDs written on a HP
DVD-Writer can be read in existing DVD players
and DVD-ROM drives. It has capacities upto 4.7
Magneto-optical rewriteable and permanent write-once
disks for optical jukeboxes and drives have capacities
ranging from 1.2 GB to 9.1 GB per disk. Manufacturers
claim it has an archival life of 100 years.
Storage solutions should integrate well with 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 interoperate in all these environments. The
current versions of NetWare, Windows, and all Unix variants
have good support for storage integration.
For instance there's HP UX 11i, which integrates well
with HP's storage systems.
Third-party storage software (like that offered by Veritas)
should also integrate well with the operating system.
One should also consider storage architectures such
as HP's ENSA-2 (Enterprise Network Storage Architecture),
HP's FSAM (Federated Storage Area Management) and IBM's
SSA (Serial Storage Architecture).
A highly available storage architecture lets you:
Store and access information on an as-needed basis.
Extend your resources through virtual capabilities.
Scale up and scale out to meet changing needs.
Simplify storage management.
Protect your data and your investment
Improve efficiency of storage systems by helping you
manage more storage with the same resources.
Careful selection of the type of storage system is another
important consideration. For this there are three technical
architectures like DAS, NAS, and SAN.
DAS (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 is the most common form of storage used by companies.
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
In DAS, I/O (Input/Output) is done in blocks from the
server to the storage. This type of 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.
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
data storage cannot rely solely on DAS, as an effective
storage strategyit has too many limitations. 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
However in a SOHO (Small Office Home Office) environment
with very few users, a DAS can handle the storage needs
NAS 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 attractive 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.
Computer 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.
STORAGE AREA NETWORKS
A 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,
banks and financial institutions, and retail manufacturing.
SAN deployments are largely driven by the use of the
FC (fiber channel) 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
and scalability, and allows large distances. 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.
SANs 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.