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Setting up SCSI on a Mac

Posted on 2003-11-17
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Last Modified: 2013-12-27
I want to set up an Ultra160 SCSI card in my Mac and have been unable to find the correct pin set up for things like Disdable Auto Spin, Disable Parity, and other settings. I know how to terminate the chain and set ID's which is done already.
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Question by:cnk_coleman
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by:lesouef
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disable autospin is on disk usually...??
what kind of SCSI card is it? Adaptec, Formac, Atto?
Maybe these settings are set by software? (usual way on PC's)
No utility shipped with it?
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by:cnk_coleman
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The card is ATTO and I also have an Adaptec 29160.

The drives are 68 pin 36LZX (36GB, 10,000rpm, SCSI3)

There is no utility for these drives and Apple will see the drives but it doesn't support these drives. I am using Intech software to format them.

I know that auto spin has to be on to get them to spin up.

But do I need "Parity disable", "TI negotiation" and "Disable Unit attention" on or off? These are done with jumpers on the drives.
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by:weed
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The jumper setup should be listed either on the top or bottom of the drive. That's where it usually is. Taking ALL the pins off should result in a working drive.
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by:lesouef
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You can enable parity at the drive level. Itr won't do any harm since this simply disable/enable parity control of the disk.
But this stays under controller choice, it simply prevents controller to use  it when disabled on disk and enabled on controller.
TI neg is probably termination negociation. In SCSI3, this works well especially with short cables, so you can leave this on.
"unit att" allows controller to allow drives to disconnect when power is on: mainly used for removeble units to sed a signal to OS, that drive has been swapped.
you can leave it on or off, no diff for a stationnary disk.
What is the make of yr disk? IBM for instance is having an excellent info mine on the web for their disk (probably gone to hitachi, since the disk activity has been sold to them)
And I heve some too here. Just let me know
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by:speyfisher
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IBM Ultrastar 36LZX (Manual PDF)

skip to:  Diagram on pg.7 and Jumper Settings pg.9
http://www.hgst.com/tech/techlib.nsf/techdocs/85256AB8006A31E587256A780052CAC5/$file/ddys-dpss_digw.PDF
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lesouef earned 50 total points
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Great, I have almost the same one in front of me (18GB model):
TI sync neg is for some Raid controllers which need to sync plates of several drives together. Leave this off for a single disk config. Only used it if Raid controller doc specifies it (not yr case)
autostart delay: leave this off as the mac may not see the 2nd drive if starting too late.
so basically, apart from SCSI ID pins (1,2,3,4), all jumpers off should be OK.
Do you have other drives on the same bus?
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by:cnk_coleman
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"Do you have other drives on the same bus?"

I have 2 on the bus. Both the same drives. They are SCA drives with the correct 68 pin adapter (for 160/320 drives) and the cable is rated for 160/320 also.

Sometimes the system will not start and recognize the startup disk. On the onboard bus I have one device and that is the CD ROM.

I have talked to IBM/Hatachi and they are no help at all. They keep telling me the way PC's need to be set up with fdisk and so on. I tell them I have a Mac and they go into the does not compute mode.

Apple is no better. They have nothing in the archives about setting up a fast SCSI chain.

These drives are used and I got them off eBay. They work great and are very fast. But I need more reliability. This is why I am posting for help. I assume that I am doing somethning wrong and I think it is the pin settings.

I also wonder if having an empty connection on the cable, like a 3 device cable and only have 2 devices on it, could be a problem.

My family machine has a IBM Ultra160 15k rpm drive in it and it works fine and runs fast. But I want a second drive in it and I am testing it out on my test system before I put it in that family machine.

Thanks for all your help so far. It gives me ideas and understanding.
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by:lesouef
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I have 2 on the bus. Both the same drives. They are SCA drives with the correct 68 pin adapter (for 160/320 drives) and the cable is rated for 160/320 also.
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Are they terminated properly? SCA drives have no termination, therefore you need one external one at the end of the cable after the last disk. With 1 disk it may work, with 2 it starts being bad, with 4, it does not work at all! This is a high freq. bus! 160Mhz is a radio freq.

Sometimes the system will not start and recognize the startup disk. On the onboard bus I have one device and that is the CD ROM.
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Watch startup time: if CD is ready before SCSI drive, it may not wait for others if on a second controller. This is correctly handled in the BIOS of a PC, not on mac. TO make a test, remove CD reader so far.

I have talked to IBM/Hatachi and they are no help at all. They keep telling me the way PC's need to be set up with fdisk and so on. I tell them I have a Mac and they go into the does not compute mode.
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not amazing...

Apple is no better. They have nothing in the archives about setting up a fast SCSI chain.
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as usual.

These drives are used and I got them off eBay. They work great and are very fast. But I need more reliability. This is why I am posting for help. I assume that I am doing somethning wrong and I think it is the pin settings.
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obviously not: this is rather binary, works or not. So this confirm the bad bus termination which is more tricky, it work erratically, it may even depend on size of the files transfered as the SCSI protocol tranfers 10 times each block before giving up; on small files, the OS has enough "patience" to accept this; on big file like 100MB, it times out.

I also wonder if having an empty connection on the cable, like a 3 device cable and only have 2 devices on it, could be a problem.
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so, this is legal, empty socket should be in the middle. Only both ends must connect somewhere and be terminated. Controller side is done automatically most of the time, drive end is up to you to do it.

I love SCSI too, and it still outperforms the cheap ATA stuff because ATA drives are rather fast, but interleaved commands are not supported, and the OS has to do everything! A SCSI disk is 50% more speed of your PC or Mac, especially with multi-tasl OS's. These are leaving the market for price reasons only. Serial ATA may be better, I have not tried it yet.

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by:cnk_coleman
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so, this is legal, empty socket should be in the middle. Only both ends must connect somewhere and be terminated. Controller side is done automatically most of the time, drive end is up to you to do it.

I love SCSI too, and it still outperforms the cheap ATA stuff because ATA drives are rather fast, but interleaved commands are not supported, and the OS has to do everything! A SCSI disk is 50% more speed of your PC or Mac, especially with multi-tasl OS's. These are leaving the market for price reasons only. Serial ATA may be better, I have not tried it yet.
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Today I will use the older non 160 rated cable with only 2 ports on it and see if that makes a difference. I do have a 160 rated terminator on the end and it seems to work but I have no way to assess that. I just have to assume that it does and is brand new.

I love SCSI also. I have had one SCSI drive fail in 10 years of fixing Mac's. The ATA drive failures could fill my workshop. I have replaced 3 this week already.

Serial ATA will be interesting although it is not as fast as SCSI. I need speed. It is nothing to transfer 500MB in one operation. I back up my data every hour to a second drive when I am working. I can't afford to loose information. I want to use the family computer to back up data to also as this will be a second backup on site.

Thanks for your help. I will try to make some changes and see if I can get it to work better.
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by:lesouef
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SCSI more reliable? I would not say so. I swapped a lot of these too (I have about 250 disks here (1/2 on servers), and it is a matter of batch; some makes are really bad, same model 3 months later is perfect.
If you need speed, why don't use you a RAID controller? that will be much better than a single drive, and be safe without wasting too much space. You need at least 3 drives to make one, but backing up every hour is a job on its own. Do you backup everything or just sync 2 volumes?
Back to yr termination pb, you don't really need something special for SCSI160, yr IBM LZX36 is only an SCSI3/LVD type, 80MB/s). So try to slow down the SCSI bus speed to 80MB/s if the board can be set for this, that may help if the controller is trying to operate it too fast; this is supposed to be automatically detected, but I have seen similar pbs before except with adaptec and symbios cards, pretty good normally.
The real test for me is to install that stuff in a PC (disk, cable and term.), and use the excellent Adaptec disk exerciser: it monitors real transfer speed: if you don't get it, there is hardware problem, otherwise, you get the specs. Unfortunately, I know no equiv. on macs.
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by:cnk_coleman
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Well I got it solved. There is a difference between OS9 and OSX on how it views SCSI. In OS9 you can have TI neogtiation on or off, it doesn't matter. But in OSX it has to be off. Same with disable unit attention which has to be enabled (default is enabled) for OSX and either for OS9.

OSX doesn't like mixed hardware. If you have a ultra160 card you will need a cable and terminator rated for ultra160 or it will give you problems.

I spent all day working on that and got it figured out

With my ATTO card and corresponding cable and terminator and the pins set right it is rock solid and no matter what I do I can't get it to crash. I had 22 apps open and was switching from Ethernet to WiFi, opening and closing files and apps, force quitting apps and much more. It never crashed once.

And it appears that you can have open spots on the SCSI chain as long as there is a correct terminator on the end. I have 2 drives and a 3 place cable.

Thanks to everyone who offed advice. It put me on the right path to get this solved.

Chuck
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