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Need help with SCSI.....so very confused.

Don Komarechka
Occasional Visitor

Need help with SCSI.....so very confused.

I need to know compatability information. I currently have a Compaq Proliant 3092 expansion running, with some 2gb and 1gb hard drives in it. Its attached to a Compaq deskpro running RedHat 9. The thing supports Fast-Wide SCSI-2, and I was wondering what my options are if I want to put in a higher capacity drive. Am I limited to only drives that say EXACTLY Fast-Wide SCSI-2, or is it flexible to something like Fast SCSI-2 ASA, or all SCSI-2? and whats Ultra2 SCSI? god....so many interfaces....
1 REPLY
Joshua Scott
Honored Contributor

Re: Need help with SCSI.....so very confused.

Here's the scoop on SCSI...

Originally, SCSI was Single Ended (SE) and used a 50-pin interface. Later someone realized that if they got a bigger cable and put 68 pins on the connector, they could double the throughput.

The biggest change occoured when they realized that they could get better throughput by making it 'differential', which means that to derive the data, the HBA compares the difference in two voltages. (this probably isn't exactly right) originally, the Voltage was 5V on the differential, and it was known as 'fast wide differential' but is now known as 'HVD' or 'high voltage differential'

now, with the new 3.3V standard, it's known as LVD or Low Voltage Differential It works the same as HVD, but because of the lower voltage was able to produce a faster throughput.

To sum up:


SCSI-1/NarrowSE = 5MB/s
WideSE = 10MB/s
SCSI-2/FWD (HVD) = 20MB/s
Ultra SCSI (LVD) = 40MB/s
Ultra2 (LVD) = 80MB/s
Ultra3/Ultra160 = 160MB/s
Ultra320 = 320MB/s

SE and all the Ultra/LVD are compatable with each other.

HVD (FWD) is not.
for a FWD interface you must use only FWD drives.

HTH.
-Josh
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