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fedora-users: Re: Fedora 15 + scsi tape drive

Re: Fedora 15 + scsi tape drive

From: Rick Stevens <ricks_at_nospam>
Date: Sat Oct 15 2011 - 01:59:38 GMT
To: Chris Adams <cmadams@hiwaay.net>, users@lists.fedoraproject.org

On 10/14/2011 11:51 AM, Chris Adams wrote:
> Once upon a time, Bill Perry <wlperry@williamperry.com> said:
>> Then I decided to upgrade. I swapped out the motherboard and got a 64
>> bit cpu and upgraded the OS (complete new install). I now have Fedora 15
>> running on the box.
> IIRC the "st" module may not be loaded automatically on newer systems.
> Try a "lsmod | grep st" and "modprobe st" (if it isn't listed). If that
> fixes it, there are several ways to get the module loaded (try that and
> post back the results).
>> It almost looks like the device changed from /dev/st4 to /dev/st0. Is
>> that possible?
> Yeah, I don't know why it would ever have been st4; the SCSI tape
> devices have always been numbered starting with 0 in my experience (I
> think I first used a SCSI tape device on Linux in 1996).

Back in the day, the SCSI controller was assigned ID 7 and typically
tape drives were given ID 4. Hard drives were usually 0, 1, 2, and 3.
IDs 5 and 6 were left for the user. Don't ask me why...I suppose they
figured no one would ever need more than four hard drives. Then again,
Gates said we'd never need more than 640K of RAM.

Older Linux kernels carried along the SCSI ID as the device name, hence
the naming of /dev/st4 on older systems. Newer kernels typically query
the device as to what it is and start assigning hard drives starting at
/dev/sda, tapes at /dev/st0 and CD/DVD drives at /dev/cdrom0 (the
"/dev/sd<letter>" bit because drives can be partitioned).

BTW, as an aside, Sun always assigned their first hard drive to ID 1.
I guess because IBM was stupid enough to assign their first floppy to
ID 1 instead of 0 on the IBM PC (aka IBM 5150) and put that bloody
twist in the floppy cable to hide that rather obvious cockup.

BTW, I was on one of the first ANSI SCSI committees (the conversion from
SASI to SCSI) and was a design engineer for (gasp! is he really
that old?) Micropolis in the mid 70s.

> An alternate way to always access a specific tape drive by a fixed path
> is via /dev/tape/by-id.

Yup. Generally /dev/st0 should get you your first tape drive, /dev/st1
the second and so on. Sorta like CD drives.
- Rick Stevens, Systems Engineer, C2 Hosting ricks@nerd.com -
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