SCSI

[meastaugh1]

Hi all, not sure this is the right forum for the topic, but it's the closest thing I could find.

Could anyone give me basic info about SCSI. I've setup a few systems with scsi adapters and devices before, but I still don't feel I fully understand it.

Will most new devices come with 50 or 68 pin connectors, or can it be either? or is one of them legacy?

Here's my question... If the scsi adapter says it's capable of about 150mbs transfer rate. and have 3 connected hdd's which are capable of 72mbs on the same channel... does that mean the transfer rate will be divided between the three devices, or will they all be able to sustain the high rate.

If I need to ensure that they reach the a high transfer rate, do I need to buy an adapter card with multiple scsi connectors?

Any help much appreciated.

 

[gargouille]

Here's a link to further understanding the issue:

http://www.transintl.com/technotes/

Scroll down to the SCSI links and follow them.

The beauty of SCSI is its ability to process multiple overlapped commands, support for command queuing and support for scatter/gather data transfers.

 

[meastaugh1]

Hi thanks for your reply.

There's one question I can't seem to find the answer for... is the transmission speed divided by the number of devices connected, or does is sustain the speed up to the maximum number of connected devices.

 

[ben64]

thats the great thing about SCSI. Multiple devices don't slow it down.

 

[JAFrank]

But.....The transfer rate for all devices is limited to that of the slowest device on the chain.

I once made the mistake of installing a brand new 29160 card with an IBM 10,000 RPM Ultra160 drive and....a Xerox 620S scanner with a max transfer rate of 10mb.

Took me a couple of hours to figure out why my shiny new drive was running so darn slow. I ended up sticking my old 2940 card back in and running the scanner off of it, which got the drive running at it's rated speed.

JAF

 

[meastaugh1]

Ahh excellent! Just wondering, as I might have to set up a PC for DV editing. The rec'd spec is to have two drives on two separate IDE channels. But since it's SCSI I can have them on the same SCSI channel. Where the min speed is 12mbs.

 

[meastaugh1]

Actually one more thing... with regard to termination...

I've picked this up and not sure if it's right... newer SCSI adapters are self-terminating... as are newer SCSI devices?

Can anyone confirm if that's right or not? many thanks

 

[edfair]

Most scsi drives have on-board termination that has to be set, usually with a jumper , or two. The rest have terminating resistors that have to be plugged.
Later host adapters are capable of self terminating. They see shat channels are in use and terminate the ones that need it. Ed Fair
unixstuff@juno.com
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