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How can you gain the cost benefits of a storage area network (SAN) without a
lot of unnecessary expense and Excedrin headaches?
Fibre channel, you say. After all, it’s the most widely used way to
connect devices and create a SAN. Besides, fibre channel provides a speed of
up to 100 Mbytes per second. The not-so-good news is that fibre channel is
expensive. Each port could cost as much as $1,000. What’s more not all
fibre channel devices can communicate with each other. You have to first hunt
around and to find those fibre channel devices that can work with each other.
To this end, testing the compatibility of devices has to rank high on your
list of must do’s before you go live.
Of course, if you had said I-SCSI as the answer the question, you
probably the type whose thinking ahead of everyone else. I-SCSI uses warm
and fuzzy TCP/IP networks to carry data. With I-SCSI, data transfers and
SCSI commands get packaged (or encapsulated) inside IP packets. Instead of
having to go through a lot of hassle and expense to put together a fibre
channel network just for storage, with I-SCSI you can use the tried and true
old network standby, Ethernet. Besides, you probably already have an
Ethernet network installed in your data center. So, forget the fibre
channel. Using SCSI commands sealed away in the IP packets lets you use
existing storage management software with little modification. Great. You
won’t have to spend hours learning some new storage management mumbo jumbo.
By using I-SCSI, you’ll get to save a lot of dollars on long distance links
between pools of storage. Some of those exotic high availability strategies
require data centers to be mirrored to locations several miles away. The
cost of running a fibre channel connection over such a distance will make you
think twice about the economics of doing this. On the other hand, I-SCSI
enables you to use existing network connections without any modifications.
You can use I-SCSI over short distances, too. Keep in mind, Ethernet
technology is moving to gigabit Ethernet, which can support up to 125 Mbytes
per second.
Of course, I-SCSI as great has it is does have one flaw, which isn’t exactly
fatal. The TCP/IP network turns out to be an inefficient way to carry data
and SCSI commands. The design of a TCP/IP network calls for maximum
redundancy over uncertain Internet connections. You can get around this
limitation by putting fibre channel in the data center and I-SCSI over long
distance links. This technique takes advantage of the best features of both
network technologies, and lets you keep your options open as far as which
technology to get tied too.
Elizabeth M. Ferrarini – She is a free-lance writer from Boston, Massachusetts.
