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Home > Archive > General Discussion > August 2002 > how many SCSI-3 devices?
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how many SCSI-3 devices?
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| XeoNoX 2002-08-29, 9:46 pm |
| What is the maximum number of devices supported by a SCSI-3 configuration? | |
| Boulware5 2002-08-29, 10:28 pm |
| 16 I believe. | |
| XeoNoX 2002-08-29, 10:37 pm |
| Thanks, but i just found found out.
Its 16 devices on a 16 bit bus, and 8 devices on an 8 bit bus. There are too many freaking SCSI drives and technical information on them to learn. | |
| xonkers 2002-08-29, 11:03 pm |
| Comptia likes to use the term 'Fast-Wide SCSI' and that is the one that is 16.
Fair warining they may ask you the question like this:
What is the highest and lowest priority on a Fast Wide SCSI?
0 lowest
0 highest
1 highest
16 lowest
7 lowest
... etc.
Personally, I know what your complaint is and I found most of my books incl Sybex and Meyers didnt really cover that very well at all.
I actually got the question..well.. I cant say it here but just take a good read on SCSI and - if something has 3 digits - would it be 7?
(Im trying not to just braindump a question here but you will know what I mean if you look it up and study it. Its something that is in Comptia's exam objectives under SCSI)
Now as to the Voodoo magic involved in assigning ID's to SCSI I will just hope someone else here can explain that one? lol | |
| Boulware5 2002-08-29, 11:07 pm |
| The highest priority is the host adapter, which is 7. It goes like this: 7,6,5,4,3,2,1,0,15,14,13,12,11
,10,9,8. | |
| XeoNoX 2002-08-29, 11:19 pm |
| How did you guess i was taking compita, as a matter of fact im looking at server+, thanks for mentioning the LUN priority.
i guess when it really cones down to it, it depends on the scsi card/controller most newer ones support 16 devices per channel - usually with the card being one of the devices on the chain (usually id#7) so 15 older cards or lower controlers at least 8 again card being one of them)
some raid and top end cards may have more than one channel (2, 3, or howmany ever chans you get) so say for example a nice mylex 2 channel raid card - 30 drives....... etc.
Someone please correct me if im wrong. | |
| azimuth40 2002-08-30, 4:43 am |
| quote:
Originally posted by XeoNoX
How did you guess i was taking compita, as a matter of fact im looking at server+, thanks for mentioning the LUN priority.
i guess when it really cones down to it, it depends on the scsi card/controller most newer ones support 16 devices per channel - usually with the card being one of the devices on the chain (usually id#7) so 15 older cards or lower controlers at least 8 again card being one of them)
some raid and top end cards may have more than one channel (2, 3, or howmany ever chans you get) so say for example a nice mylex 2 channel raid card - 30 drives....... etc.
Someone please correct me if im wrong.
OK not wrong but maybe a possible confusion. LUN is Logical Unit Number. This is not the same as the SCSI ID which is what Boulware5 gave you in his reply. LUN is three bits that can be sent to a SCSI ID to point to 8 additional units that the ID itself controls. An example would be an external CDROM tower with up to 8 drives in it. The tower would have one SCSI ID and 8 LUN's.
Multiple channels on an SCSI host adapter follow the same rules as single channel with the exception that the card itself still normally takes one ID so a Wide card with two channels would support 15 ID's on one channel and 16 on the other for 31 available ID's then each of those ID's could have 8 LUN's.  I believe that when you have LUN's then the terms "initiators" (the ID) and "targets" (the LUN's) are used.
I see alot has been going on while I was on holiday so this was an easy one. | |
| xonkers 2002-08-30, 4:52 am |
| whoa... what that last guy just said.
I hope there isnt a pop-quiz later lol
All I know is that I went with
0 is the highest
15 is the lowest
I had it right, and took the cert and ran!
On the jumper block question I didnt really understand how to explain it but I just knew that with 3 numbers there it had to be 7.
This is now way over my head but very interesting stuff. I just wanted to clarify that Comptia uses certain 'terms' like Fast-wide SCSI and Im pretty sure they dont go further than that. Mostly they are just SCSI-2 or regular old school SCSI questions.
In which case think
0 highest
7 lowest
Thats my low-budget SCSI tipperoo of the day
Thanks for the awesome tips on this one you guys! | |
| thecomeons 2002-08-30, 4:53 am |
| does anybody else think that scsi could be on the way out? apples used to be solely scsi, but have started to use ide and firewire over this last few years. perhaps firewire will soon be used internally for drives and support raid. (though does that mean a pc would still need to have an ide hd to boot from and load drivers for firewire support? ah, maybe that will be implimented in the bios.) | |
| xonkers 2002-08-30, 5:22 am |
| This is what Ive heard
In six years time an entirely new computer hits the market -Intels hyperspeed CPU - All firewire everything inside and all USB outside. Guess who is gonna have the new OS for it? Yup! (codenamed Cypress)
It will not be backwards compatible with anything now.
Bad news for A+ people - It will look like a car battery and almost have no reason to be taken apart as everything from NIC to DIMMS/PCMCIA (whatever they are called then) will somehow plug n play.
Like TV repairmen - gone to a world where its cheaper just to get a new one 'block' or just buy new peripherials for it.
You heard it here first people. At least thats what my 'sources' tell me anyway. It really is all totally possible but just the marketing is left. |
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