SCSI Questions, From IBM.PC.FAQ:

* What's the difference between SCSI and SCSI-2? Are they compatible?
* How am I suppose to terminate the SCSI bus?
* Can I share SCSI devices between computers?

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* What's the difference between SCSI and SCSI-2? Are they compatible?

The main difference between SCSI and SCSI-2 are some new minor 
features that the average person will never notice.  Both run at a 
maximum 5M/s.  (note: Fast and Wide SCSI-2 will potentially run at 
faster rates).  All versions of SCSI will work together.  On power 
up, the SCSI host adapter and each device (separately) determine the 
best command set the speed that each is capable of.  For more 
information on this, refer to the comp.periphs.scsi FAQ.

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* How am I suppose to terminate the SCSI bus?

Some basic rules on termination:
1. The SCSI bus needs exactly two terminators, never more, never less. 
2. Devices on the SCSI bus should form a single chain that can be 
traced from the device at one end to the device at the other.  No 
'T's are allowed; stub length should be kept as short as possible.
3. The device at each end of the (physical) SCSI bus must be 
terminated, all other devices must be unterminated.
4. All unused connectors must be placed _between_ the two terminated 
devices.
5. The host adapter (controller) is a SCSI device.
6. Host adapters may have both an internal and external connector; 
these are tied together internally and should be thought of as an 
"in" and "out" (though direction has no real meaning).  If you have 
only internal or external devices, the host adapter is terminated 
otherwise it is not.
7. SCSI ID's are logical assignments and have nothing to do with 
where they go on the SCSI bus or if they should be terminated.
8. Just because your incorrectly terminated system happens to work 
now, don't count on it continuing to do so.  Fix the termination.
Examples:

      internal      external           internal            external
    T------|-----|------T          T------|-------|-----|------|------T
 drive   drive   HA    cdrom      tape  unused unused   HA   drive  drive

        internal             external             external
     T------|-----T      T------|------T          T------T
   drive  drive   HA     HA    tape   cdrom       HA    cdrom

"T" = terminator   "|" = connector (no terminator)   "HA" = Host Adapter

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* Can I share SCSI devices between computers?

There are two ways to share SCSI devices.  The first is removing the 
device from one SCSI host adapter and placing it on a second.  This 
will always work if the power is off and will usually work with the 
power on, but for it to be guaranteed to work with the power on, your 
host adapter must be able to support "hot swaps" - the ability to 
recover from any errors the removal/addition might cause on the SCSI 
bus.  This ability is most common in RAID systems.
  The second way to share SCSI devices is by connecting two SCSI 
busses together.  This is theoretically possible, but difficult in 
practice, especially when disk drives are on the same SCSI chain.  
There are a number of resource reservation issues which must be 
resolved in the OS, including disk caching.  Don't expect it to 'just 
work'.

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