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SAN
Overview
Fulfilling a Demand
Storage Area Networks (SANs)
are revolutionizing information storage and management in the
same way that Local and Wide Area Networks (LANs/WANs) transformed
information sharing across the enterprise. As storage capacity
continues to grow at a dramatic annual growth rate, so do the
demands for external storage under centralized management. To
properly satisfy these demands, a minimum of features, including
continuous data availability, resource sharing, system scaleability,
and ease of management are all required.
Both SAN and Network Attached Storage (NAS) architectures are
the current prime candidates used to fulfill these requirements.
Although the main focus of this paper is to provide a general
introduction to SAN, a comparison of SAN and NAS is also included.
Defining the Generic SAN
A typical SAN can be defined as a network containing at least
two servers that have access to a storage pool through an interconnection
with at least one hub or switch. It is necessary that the technologies
used in this network are high-performance, high-reliability
and scaleable in order to achieve that combination of the speed
expected of a traditional storage environment, with the connectivity
of networking.
With a successful implementation, a SAN enables fast, reliable
access among servers and external or independent storage resources,
and provides a network where storage resources appear generic
and are shared by the servers, rather than being dedicated to
any one server.
SAN Advantages
There are several, most-commonly discussed advantages that a
SAN has over using a single network for all applications:
- Centralized Storage
- Since SAN resource management is centralized, physical
storage devices are virtually isolated from what the client
can see. This "big-picture" management results
in better use of the disk and tape resources and allows
more flexibility for distributing and reconfiguring resources.
- Superior Connectivity
- Every server on the network (or any storage device with
enough intelligence) can address all of the (other) storage
devices on the network, for distances up to 10 kilometers
(with Fibre Channel support). Storage resources that may
be scattered throughout a building, or several buildings,
may be accessed for purposes of mirroring or clustering,
etc.
- LAN-Free & Server-Free Backup
- By providing a separate channel for data, a SAN can offload
backup traffic from the LAN. Backup can be performed outside
of the LAN, with the data moving from the storage device
to the server. The server then retransmits the data through
the SAN to a SAN-connected library. This setup is referred
to as LAN-free backup. Server-free backup is also possible,
where the data is moved across the SAN from one storage
device directly to another. The server initiates the backup
command, but the data moves directly between the storage
devices through the SAN, without further involving the server
or the LAN.
- Scaleability
- By removing general-purpose traffic (end-user data such
as e-mail, etc.) from the network, the SAN servers and storage
devices can dedicate resources to managing and supporting
only I/O traffic. Since ongoing operations are not affected,
storage capacity can grow and storage performance can improve.
SAN vs. NAS
Both SAN and NAS technologies involve externalizing storage
from the server and adding flexibility to network storage. With
SAN technology, the storage devices all reside on their own
networks, along with all of the flexibility and performance
benefits associated with networking. NAS technology, however,
involves the use of a networking interface for the storage devices,
which make them each an active node on the existing network.
Both technologies have their appropriate benefits, drawbacks,
and applications.
One of the big differences between a SAN and a NAS is that NAS
devices typically see storage as files; SANs usually see blocks
of data. This difference is one of the major advantages of NAS
configurations; allowing them to be easy to install and to also
provide low-cost entry product configurations that use an already-available
and proven technology.
SANs offer a high-bandwidth link capable of growing incrementally,
making them especially well suited for transferring very large
blocks of data. NAS networks, however, are known for bandwidths
suited to efficiently move data in moderate-size segments. Whereas
SAN delivers data reliably and in a predicted amount of time,
NAS (and LANs) can retransmit data when the network is congested
or fails.
Since NAS is file-oriented, it works well for document management
applications, but it is not as ideal for database applications.
By holding files for the network, a NAS is very flexible, although
this same feature can cause the NAS to be inefficient at peak
times if the network is slow. For these reasons, NAS devices
are best suited for workgroups with high storage demands and
in cluster server environments.
It is apparent that both architectures have their advantages,
depending on the specific application. The main advantages of
NAS relate to the way it allows use of existing networking infrastructures
and the investment already made to the networking industry.
Due to standardization and compatibility issues, SANs could
possibly take a couple more years to offer a heterogeneous data-sharing
environment on a widespread commercial basis. SAN and NAS are
somewhat complementary technologies that are expected to coexist
for some time, with several current NAS functions likely to
eventually migrate to the SAN.
The StorCase® SAN Plan
Until the continually changing SAN standards and long-term interoperability
of standardized configurations stabilize, SAN solutions will
continue to be available only in proprietary configurations.
In keeping with the philosophy of providing flexible, mix-and-match
storage products, StorCase has elected to offer an open architecture
storage design, allowing users to retain the freedom to select
an array of tested components with features that best meet the
needs of their specific application(s).
StorCase is currently testing InfoStationTM, a new
SAN-compatible enclosure that will integrate quality SAN components
from several popular SAN manufacturers. When InfoStation SAN
testing is completed, StorCase plans to offer several OSA-recommended
solutions to choose from, all which feature the intelligent,
self-monitoring InfoStation backplane enclosure. Visit us on
the WEB for more information about the StorCase InfoStation.
Summary
There is clearly a demand for external storage that is centrally
managed and capable of performing with the benefits of the latest
system technologies. Both SAN and NAS architectures can meet
this demand, and both have their advantages for specific applications.
Until SAN standardization and compatibility issues become stable,
SAN and NAS, which are somewhat complementary configurations,
are expected to coexist for some time. In keeping abreast of
current trends in technology, StorCase is currently designing,
manufacturing and testing new products with SAN compatibility
as a major priority.
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