Jumper setting on external SCSI Hard Drive - Storage

This is a discussion on Jumper setting on external SCSI Hard Drive - Storage ; I am installing an older IBM 50-pin SCSI hard drive in an external case on an older power Mac. I have the chain full of peripherals at present. I thought if I were to look at the present drive coming ...

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Thread: Jumper setting on external SCSI Hard Drive

  1. Jumper setting on external SCSI Hard Drive

    I am installing an older IBM 50-pin SCSI hard drive in an external case
    on an older power Mac. I have the chain full of peripherals at present.
    I thought if I were to look at the present drive coming out of the box
    that I could figure out how to configure the jumper settings. However
    the IBM hard drive has more and differently labeled jumper positions.
    I have confirmed that I need to do the following:
    - Enable parity checking
    - Enable auto start
    - Disable sync negotiation
    - Disable write protect
    - Set the SCSI ID internally to a number between 1 and 6 not already
    being used (i.e. I will set it to the number that this hard drive is
    replacing) I need to set it internally for the box has no external
    switch for ID setting.
    The two settings I can not find what to do with are:
    - Unit attention
    - Termination power
    Am I to assume that one of the peripherals on a chain needs to have
    termination power enabled to give current to the chain? Or is it
    provided from the computer since the chain involved the CPU and
    internal CD and Hard drive as part of the chain? If I have the
    termination power on and it is not needed could that damage anything?


  2. Re: Jumper setting on external SCSI Hard Drive

    "DJW" writes:
    >
    > I am installing an older IBM 50-pin SCSI hard drive in an external case
    > on an older power Mac. ...
    > I have confirmed that I need to do the following:
    > - Enable parity checking
    > - Enable auto start


    You might be able to leave auto-start disabled for a Mac.

    With auto-start disabled, the drive doesn't spin-up until the computer
    tells it to. On most PCs, this never happens, but I think Mac firmware
    (especially on those Macs with built-in SCSI) will send the command.

    If it works, I consider this a good idea. The startup-draw of many
    devices starting simultaneously can sometimes overload a circuit. With
    auto-start disabled, it's startup will happen after the other devices.

    > - Disable sync negotiation
    > - Disable write protect
    > - Set the SCSI ID internally to a number between 1 and 6 not already
    > being used (i.e. I will set it to the number that this hard drive is
    > replacing) I need to set it internally for the box has no external
    > switch for ID setting.


    Ugh. I can't stand SCSI cases without any ID selectors....

    > The two settings I can not find what to do with are:
    > - Unit attention
    > - Termination power


    I'd leave both of these set to the factory default. Hopefully, the
    diagram that has identified these pins also says what the defaults are.

    I don't know what Unit attention is, so I can't help with that one.

    Termination power is what the name implies - it tells the drive to
    provide power on the SCSI bus for the purpose of driving a terminator.

    SCSI terminators (especially active ones) require a power supply to
    work. Some device (any device) on the bus may supply this power, but
    something has to (or you'll need a power brick for your terminator,
    which is a pain in the neck.) A lot of computers and SCSI host adapters
    provide this. Many drives do as well, but there's no guarantee.

    If the drive is jumpered to provide termination power and you don't need
    it, it probably won't damage anything. The only exception I can think
    of goes back to the old Adaptec 1542 cards. Those cards had a fuse on
    the termination power line. That fuse could blow if more than five
    devices were providing termination power at once.

    In general, I'd leave term power turned off unless you find that you
    really need it (because no other device is.)

    -- David

  3. Re: Jumper setting on external SCSI Hard Drive

    By what I can remember the last time I was in my computer's box I saw
    that termination power was jumped (enabled on?) on the internal CD. I
    use an active terminator device on the last scsi peripheral so I guess
    you are saying if I need the power set on I will not see the led lamp
    on the terminator device lit?

    On Jan 23, 2:37 pm, sham...@techie.com (David C.) wrote:
    > "DJW" writes:


    > Termination power is what the name implies - it tells the drive to
    > provide power on the SCSI bus for the purpose of driving a terminator.
    >
    > SCSI terminators (especially active ones) require a power supply to
    > work. Some device (any device) on the bus may supply this power, but
    > something has to (or you'll need a power brick for your terminator,
    > which is a pain in the neck.) A lot of computers and SCSI host adapters
    > provide this. Many drives do as well, but there's no guarantee.
    >
    > If the drive is jumpered to provide termination power and you don't need
    > it, it probably won't damage anything. The only exception I can think
    > of goes back to the old Adaptec 1542 cards. Those cards had a fuse on
    > the termination power line. That fuse could blow if more than five
    > devices were providing termination power at once.
    >
    > In general, I'd leave term power turned off unless you find that you
    > really need it (because no other device is.)
    >
    > -- David



  4. Re: Jumper setting on external SCSI Hard Drive

    In article , David C. wrote:
    > You might be able to leave auto-start disabled for a Mac.
    >
    > With auto-start disabled, the drive doesn't spin-up until the computer
    > tells it to. On most PCs, this never happens, but I think Mac firmware
    > (especially on those Macs with built-in SCSI) will send the command.

    My PCs Adaptec AHA2940UW will send the command. I have my
    devices start in sequence to give my PS a chance to catch up. (they
    are FULL hight SCSI 5 1/4" disks here!)
    I got a Seagate 1GB in my mac performa that also defaults to
    this. I haven't had a problem

    --

    From the Desk of the Sysop of:
    Planet Maca's Opus, a Free open BBS system. telnet://pinkrose.dhis.org
    Web Site: http://pinkrose.dhis.org, Dialup 860-618-3091 300-33600 bps
    The New Cnews maintainer
    B'ichela


  5. Re: Jumper setting on external SCSI Hard Drive

    In article <1169592757.025094.111380@a75g2000cwd.googlegroups. com>, DJW wrote:
    > By what I can remember the last time I was in my computer's box I saw
    > that termination power was jumped (enabled on?) on the internal CD. I
    > use an active terminator device on the last scsi peripheral so I guess
    > you are saying if I need the power set on I will not see the led lamp
    > on the terminator device lit?

    If No light, you need term power.

    --

    From the Desk of the Sysop of:
    Planet Maca's Opus, a Free open BBS system. telnet://pinkrose.dhis.org
    Web Site: http://pinkrose.dhis.org, Dialup 860-618-3091 300-33600 bps
    The New Cnews maintainer
    B'ichela


  6. Re: Jumper setting on external SCSI Hard Drive

    B'ichela writes:
    >>
    >> With auto-start disabled, the drive doesn't spin-up until the computer
    >> tells it to. On most PCs, this never happens, but I think Mac firmware
    >> (especially on those Macs with built-in SCSI) will send the command.

    > My PCs Adaptec AHA2940UW will send the command. I have my
    > devices start in sequence to give my PS a chance to catch up. (they
    > are FULL hight SCSI 5 1/4" disks here!)


    Many Adaptec cards will send the command, but you often have to
    explicitly configure this using the card's setup screen (typically
    accessed by pressing a hot-key during the boot sequence.)

    I haven't used a 2940, but the cards I have used came with this disabled
    from the factory.

    I remember tracking down several "my system won't boot" problems to a
    drive with auto-start disabled and a SCSI card that doesn't send the
    startup command.

    -- David

  7. Re: Jumper setting on external SCSI Hard Drive

    "DJW" writes:
    >
    > By what I can remember the last time I was in my computer's box I saw
    > that termination power was jumped (enabled on?) on the internal CD. I
    > use an active terminator device on the last scsi peripheral so I guess
    > you are saying if I need the power set on I will not see the led lamp
    > on the terminator device lit?


    That would be right. If your terminator has a light, and the light is
    on, then some device is sending termination power to the bus.

    -- David

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