This is part of The Pile, a partial archive of some open source mailing lists and newsgroups.
Subject: [OT] Scsi Termintation From: Ahbaid Gaffoor <ahbaidg@worldnet.att.net> Date: Sun, 03 Sep 2000 13:28:10 -0700 Hi all, I'm almost doen building my linux - oracle database server... Just one question for the SCSI experts. The board is a supermicro P6DBS with an onboard adaptec SCSI controller. I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50 pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that can handle seven devices. Here's the plan: Let's say the cable is numbered from the motherboard connector to the last device on it as 0 through 7. I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6 and 7 unattached. Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the drive on 5 can be made to terminate, is that what I should do? Your advice is all welcome. thanks, === Subject: Re: [OT] SCSI LVD Cables From: John Aldrich <john@chattanooga.net> Date: Sun, 3 Sep 2000 14:15:58 -0400 On Sat, 02 Sep 2000, Ahbaid Gaffoor wrote: > Hi, > > what does the LVD thing mean when talking about SCSI? > > Is it something analagous to 66/Mbs IDE? > > If so, is it's use supported under Linux? > It depends entirely upon the controller and the hard drive and has nothing to do with the operating system, AFAIK. If your SCSI controller is supported under linux, I think that LVD will work with linux. LVD==Low Voltage Differential, AKA (I think) Differential SCSI. Your hard drives MUST be LVD drives, your controller has to be an LVD controller and I think you may also need special cables. You will *definitely* need different termination, if termination isn't built-in as an option on your last LVD device. === Subject: Re: [OT] Scsi Termintation From: Ahbaid Gaffoor <ahbaidg@worldnet.att.net> Date: Sun, 03 Sep 2000 14:00:26 -0700 Any advatnges or disadvantages of setting the SCSI id's on the devices as they progress along the cable? That is, first device from controller - SCSI ID 0 (The cd-rom, first connector) Second device - SCSI ID 1 ( the first drive, second connector) Third Device - SCSIS ID 2 (the second drive, third connector) etc. Or can I just place them anywhere along the cable? I tend to think that it is easier to keep track of things by placing them in order... regards and thanks, your answer has cleared things up a lot. === Subject: Re: [OT] Scsi Termintation From: John Aldrich <john@chattanooga.net> Date: Sun, 3 Sep 2000 15:13:12 -0400 On Sun, 03 Sep 2000, Ahbaid Gaffoor wrote: > Hi all, > > I'm almost doen building my linux - oracle database server... > > Just one question for the SCSI experts. > > The board is a supermicro P6DBS with an onboard adaptec SCSI controller. > > I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50 > pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that > can handle seven devices. > > Here's the plan: > > Let's say the cable is numbered from the motherboard connector to the > last device on it as 0 through 7. > > I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6 > and 7 unattached. > > Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the > drive on 5 can be made to terminate, is that what I should do? > Put the last device on position 7 and use the on-board termination, if available. Otherwise, put it on 6 and use a terminator. === Subject: Re: [OT] SCSI LVD Cables From: wyrd <wyrd@triskelion-nova.com> Date: Sun, 03 Sep 2000 12:33:47 -0700 Your hard drives MUST be LVD drives, your controller > has to be an LVD controller and I think you may also need > special cables. That's not entirely true. I had an LVD drive in use for quite awhile on a non-LVD controller. Some drives have jumpers that allow them to be used in an existing system. There are also adapters available. ~Rob === Subject: Re: [OT] Scsi Termintation From: "Mikkel L. Ellertson" <mikkel@Infinity-ltd.com> Date: Sun, 3 Sep 2000 15:37:22 -0500 (CDT) On Sun, 3 Sep 2000, Ahbaid Gaffoor wrote: > Any advatnges or disadvantages of setting the SCSI id's on the devices as they > progress along the cable? > > That is, first device from controller - SCSI ID 0 (The cd-rom, first > connector) > Second device - SCSI ID 1 ( the first drive, second connector) > Third Device - SCSIS ID 2 (the second drive, third connector) > etc. > > Or can I just place them anywhere along the cable? > > I tend to think that it is easier to keep track of things by placing them in > order... > > regards and thanks, > > your answer has cleared things up a lot. > > Ahbaid. > Well, the device number actualy affects who gets the SCSI bus if more then one device want it at the same time. The higher the number wins. You would think because of this that you would want the hard drives to have the highest numbers, but this is not the case. Hard drives are usualy not time critical when sending/recievign data - that is what they have buffers for. Tape drives tend to have tighter timing requirments. Also, it is normal practice to make the hard drive you are going to boot from ID 0. (Some older hardware requires that you boot from ID 0.) ALso, if you change SCSI IDs, you may change the mapping of your hard drives under Linux. Linux maps the first SCSI hard drive it finds to /dev/sda, the second to /dev/sdb, and so on. It does the same kind of mapping for other SCSI devices. So if your SCSI CD is device 0 now, and you deside to add another hard drive later, and put it as ID 0 because you are plugging it in where the CD drive was, it now becomes /dev/sda. Now your /etc/fstab is out of sync with your physical drives. Lots of fun. NOw, if you were using a older Sparc Station, you would want the CD as ID 6, and if you have a SCSI tape, you want that as ID 5. This is because the boot PROM on expects them there by default. You can do things like boot CDROM or boot TAPE with them. === Subject: Re: [OT] SCSI LVD Cables From: John Aldrich <john@chattanooga.net> Date: Sun, 3 Sep 2000 20:24:05 -0400 On Sun, 03 Sep 2000, wyrd wrote: > > Your hard drives MUST be LVD drives, your controller > > has to be an LVD controller and I think you may also need > > special cables. > > That's not entirely true. I had an LVD drive in use for > quite awhile on a non-LVD controller. Some drives have > jumpers that allow them to be used in an existing system. > There are also adapters available. > Thanks for setting me straight. I was under the impression you had to have an LVD drive with an LVD controller. :-) My SCSI knowledge is somewhat limited by what more knowledgeable people have told me in the past. My understanding was as I'd mentioned previously. :-) John === Subject: Re: [OT] SCSI LVD Cables From: "M. Neidorff" <neidorff@bellatlantic.net> Date: Sun, 03 Sep 2000 20:55:48 -0400 At 12:33 PM 09/03/2000 -0700, you wrote: > > Your hard drives MUST be LVD drives, your controller > > has to be an LVD controller and I think you may also need > > special cables. > >That's not entirely true. I had an LVD drive in use for >quite awhile on a non-LVD controller. Some drives have >jumpers that allow them to be used in an existing system. >There are also adapters available. My experience, I've just added a LVD drive to an ultra scsi system. The drive (seems to) have stepped down seamlessly to ultra scsi speed and work fine. The drive is terminating itself (I didn't do a thing to make it terminate). === Subject: Re: [OT] Scsi Termintation From: "M. Neidorff" <neidorff@bellatlantic.net> Date: Sun, 03 Sep 2000 21:07:29 -0400 At 03:13 PM 09/03/2000 -0400, you wrote: >On Sun, 03 Sep 2000, Ahbaid Gaffoor wrote: > > Hi all, > > > > I'm almost doen building my linux - oracle database server... > > > > Just one question for the SCSI experts. > > > > The board is a supermicro P6DBS with an onboard adaptec SCSI controller. > > > > I have four seagate ST12550N 50 pin SCSI drives, and the board has a 50 > > pin interface. I also have a 50 pin SCSI cd-rom and a 50 pin cable that > > can handle seven devices. > > > > Here's the plan: > > > > Let's say the cable is numbered from the motherboard connector to the > > last device on it as 0 through 7. > > > > I plan to put the cd-rom on 1, the four drives on 2 through 5, leaving 6 > > and 7 unattached. > > > > Do I need to get a SCSI terminator? If so, do I put it on 6? Or, if the > > drive on 5 can be made to terminate, is that what I should do? > > >Put the last device on position 7 and use the on-board >termination, if available. Otherwise, put it on 6 and use a >terminator. There are 3 things to keep in mind: position, SCSI ID and termination. First, position doesn't matter. (we are dealing with signals near the speed of light here) SCSI ID is important. Each device must have a unique ID, in your case 0 - 7. It is settable through either jumpers or some other mechanism on the device itself. The controller usually is ID #7 and its best to just let this be. Beyond that, it doesn't matter what ID you give other devices. Termination is very important. You may be dealing with older scsi devices in which case they may or may not have built in termination. If they do have the built in termination, it may or may not be good enough (isn't this wonderful!!!). You are going to have to check the pinouts and figure it out for each drive and device. The ones at the physical ENDS of the scsi chain MUST, MUST, MUST be terminated. If the controller is the end of the chain (you are just using the internal or external cable connection) then the controller must be terminated. If you are using both the internal and external connections, then the controller must be un-terminated and the device at the end of the chain must be terminated. Again, you are going to have to hit the docs of the controller to see what is what for the built in termination. ===