SCSI Device ID Priority

[Cowboy]

How should the priority (ID) of the SCSI devices be set in a chain, or does it matter. My Tekram DC315U Controller is set at 7 and should be the highest priority my CD-RW, CD Rom, and scanner then follow as 6, 5, and 4 respectively. Is this the correct way to assign the priority or should they be reversed.

During boot up it appears as though the SCSI card finds them in reverse order.

 

[Zipperhead]

cause it loks for them in ascending order 0,1,2,3,4,etc.if you had a scsi h.d. you would want that to be 0.

Zip

 

[Cowboy]

Thanks, but do I have them set in the right order or do they need to be reversed?

 

[Cyph3r]

The SCSI ID's are NOT priority as you are thinking. But rather a way of differentiaing devices. The old SCSI I and early SCSI II controllers only allowed for 7 devices. So Device 0 was deemed and continues to be deemed the bootable drive, allowing for the reaming 5 device ID's to be used for anything else, while 7 was reserved for the SCSI controller itself.

With the newer SCSI III controllers..they support up to 15 devices. Usually the SCSI controller still sits at 7 and that's fine. The HD from which you wish to boot must be set to ID 0, from there on, you can setup your remaining devices on any ID you choose.

I currently have 3 SCSI III Ultra2LVD ID's, at ID 0, 1 and 2. My Plextor CD-ROM is sitting at ID 6 and my SCSI controller is sitting at ID 7.

Just like on a IDE system you must designate one device as a master and another a slave on the chain, with SCSI you must designate a unique ID to differentiate the devices. If you plug 2 devices with the same ID, then you're going to see some very bizzare behaviour..Regards

 

[maddmax]

In Adaptec scsi bios you can boot from any bootable device ID. I'm running a dual boot system and switch boot devices in the scsi bios. FWIW

 

[jimmygates]

I think there is a priority in Windows when you set SCSI ID on cards. I read somewhere devices on the lower end of the chain would get first priority (I guess first priority to data?) compared to devices higher on the ID chain.



-Jimbo