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Gerhard den Hollander
* Peter B Van Campen
(Thu, May 08, 2003 at 10:12:08AM -0500) Dear Ronc,
The Adaptec 2940U2W can handle 15 connected SCSI devices plus itself, making 16 SCSI ids. Why do you need 2 SCSI controllers? You could put all the listed devices on one card and not even have to re-plug the SCSI ids.
Couple of reasons I can think of. If one of the devices is narrow, you can only have 7 devices on the chain, and the chainlength (including internal cabling) is limited to 3Meters.
The adapter determines the maximum number of devices. Having narrow (8 bit) devices on the bus has nothing to do with it, other than that no more than 7 narrow devices can be on the bus, along with another 8 wide devices. Maximum cable length depends on whether the system is LVD or single-ended and the bus speed.
Also if you have one (or more) narrow devices, they will drag down the bus speed, in which case it makes a lot of sense to have 2 cards, one with the narrow disk and somce slower devices (tapedrives, cd, dvd &c) and use the other card for high performance devices.
Perhaps. Good SCSI adapters allow setting individual bus speeds for each device, so a slow device that is seldom used will have no effect on the bus speed (except when it is being used). -rex