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A closer look at the
15K.3 Is installing a SCSI
hard drive difficult? Are there special jumpers or settings? We are about
to take a closer look at the Seagate Cheetah 15K.3 to find out! Those of you
who already have SCSI experience will already know that there are some
basic SCSI rules to follow. However, if you just learning or reeducating
yourself, you should pay close attention to this page.
At a distance, the
15K.3 looks like any other hard drive. However, once you look at it up
close you will find that there are many more jumpers to play with than
the standard IDE hard drive. With IDE hard drives, the most you need to
worry about is setting the jumpers for Slave or Master. With this
particular SCSI hard drive, there are 16 different SCSI IDs; 0 through
15. There is also no such thing as Slave or Master settings. Now don't
panic, setting a SCSI ID is just as easy as setting an IDE hard drive to
Slave or Master. In fact, I think it's easier. You simply follow the
handy little SCSI ID chart in the directions and move a few jumpers (if
necessary). The drive comes with the SCSI ID set to 0, so if you are
only running one device, you don't need to change a thing. However, if
you are running multiple SCSI drives and devices, you must assign a
unique SCSI ID number to each device. Remember, SCSI interface cards
also require a SCSI ID number which is almost always #7. Don't forget
that SCSI arrays require a SCSI Terminator at the end of the drive
chain. Some drives have a built in SCSI terminator, unfortunately, this
drive does not. Lucky for me, the SCSI cable that came with my SCSI
interface card has a built in terminator on the end.
One interesting feature
of the "LW" model of the 15K.3 is that it has an extra SCSI ID block
called "J5". Some cases have a remote SCSI ID cable that connects to the
J5 block so that the user can set the SCSI IDs externally. I can see how
the J5 block would be handy, especially in rack mounted servers.
The SCSI I/O connector, J5 Block
and 4-Pin DC Power
Another very important
factor is knowing if your SCSI devices operate in "single-ended" (SE) or
"low voltage differential" (LVD) mode. The performance between the two
is huge, with LVD being the best performer. Whatever you do, remember to
NEVER use an SE device on the same SCSI channel as your LVD devices or
the performance of your SCSI array will drop severely. If you install an
SE device on the same SCSI channel as your LVD devies, the SCSI
controller will automatically drop data transfer down to SE levels
across the entire SCSI channel. This is a very interesting fact that I
had not been aware of from my early days of running SCSI. Just keep this
little factoid in the back of your head when purchasing a SCSI interface
card. It may be a good idea to purchase a two channel SCSI interface
card or just two cards If you have both SE and LVD devices. The 15K.3 is
a high performance LVD device and you don't want to retard it's
performance by adding a SE device on the same SCSI channel.
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