Lennox Hearth D2 warranty Fundamental Scsi rules

LaCie d2 SCSI AIT Drive	Technical Information
	page 17

LVD (Low Voltage Differential) – This latest addition to the SCSI interface, which became important with Ultra2 SCSI, combines all of the advantages of SE and HVD. LVD has rapidly become the de facto standard in high-performance SCSI. Its benefits include increasingly lower cost, more and more widespread use, enhanced reliability, higher data transfer rates, compatibility with the newest high-speed hard drives, longer cable lengths than SE (up to 12 m), and backwards compatibility with older SCSI technologies.

The following table shows the different types of SCSI implementations:

Category	Narrow (8 bit)	Wide (16 bit)	Wide (16 bit)	Wide (16 bit)	Wide (16 bit)
SCSI types	Fast SCSI	Ultra Wide SE	Ultra2 Wide (LVD)	Ultra 160 (LVD)	Ultra 320 (LVD)
Transfer rate	10MB/s max	40MB/s max	80MB/s max	160MB/s max	320MB/s max
# of devices	8 max	16 max	16 max	16 max	16 max
Cable length	3 m max	1.5 m max	12 m max	12 m max	12 m max
Connectors	25 or 50-pin	68-pin	68-pin	68-pin	68-pin

Fundamental SCSI rules

Follow these seven basic rules when setting up your SCSI peripheral or chain.

1)Give each SCSI peripheral a unique ID number.

Each device in your SCSI chain needs a unique ID number, either from 0 to 6 for Narrow SCSI, or any number between

0-6 and 8-15 for Wide SCSI (ID 7 is generally reserved for your computer’s SCSI controller). No two devices in the same chain may have the same ID number, but the order in which the devices are connected in the bus does not matter. For example, the device with ID 2 could be physically located at the end of the chain, while the device with ID 6 is connected directly to the SCSI port of your computer.

2)Always terminate your SCSI chain.

The last device in your SCSI chain must be terminated. Even if you have only one SCSI peripheral in your chain, you must terminate it. Single-ended SCSI devices may have an internal terminator (using an on/off switch) or may require an external terminator.

Warning! LVD buses always require external termination; they do not have internal terminators. Therefore, the last LVD device in a chain must have an external terminator. Consult your computer supplies specialist for a terminator that meets your needs.

3)Avoid mixing LVD and SE devices in the same SCSI chain.

For performance reasons, it is important to not mix LVD and SE devices on the same chain. An all-LVD or all-SE chain will generally perform more reliably than a mixed chain. While it is technically possible to mix LVD and SE devices on the