BSD/Darwin Names of Hard Disk Drives

Question

BSD/Darwin Names of Hard Disk Drives

Hello! A question just out of curiosity:
In what order does Mac OS X assign names/numbers to the system's hard disks?

I am wondering because I mounted an old 2.5" inch drive (originally from my tangerine iBook) formated as MBR/FAT32 into a G4-533 (digital audio). The 2.5" jumpered as slave/secondary and the 3.5" boot drive as master/primary (parallel-ATA of course).

The first time I stated up, the 3 GB small FAT-formated laptop-drive got BDS/Darwin-name disk0 and my 60GB boot drive got disk1.

However, after I reinitialized the small 3GB to ApplePartionTable/MacOS Extended and rebooted again it became disk1 and my boot-drive got disk0 - as previously awaited.

Do somebody know the rules MacOS is using when assigning disk names/numbers?
Thanks for feeding my curiosity.
Regards A.

G4 etc., Mac OS X (10.3.x)

Posted on Feb 27, 2011 9:46 AM

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Answer 1

Feb 27, 2011 9:58 AM in response to Aaron d´Europe

Short addition: OS is 10.5.8 Leopard not Panther as mentioned in my prev. sig-line.
I know it is unsupported on a 533 MHz-G4 but nevertheless runs great with the exception of some graphic glitches.

a.

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Answer 2

Kappy

Level 10

362,007 points

Feb 27, 2011 10:43 AM in response to Aaron d´Europe

The most likely explanation is that the drive's state was undetermined or you booted from the old drive. Also depends on how the G4 normally assigns IDs: Master/Slave or Cable Select. If the latter than the ID depends on where the drive is located on the cable. If the former then by how each drive is jumpered.

The first drive seen by a Unix system is assigned disk0. However, Unix really doesn't care which is a boot drive. Drives are simply assigned an ID as they are initially discovered during startup. Usually the default boot drive will be assigned disk0.

Disk names on the other hand are simply an alias created by OS X to retain a similarity to older versions of Mac OS. Human naming makes things a bit easier on the user who typically does not even know that OS X is actually a windowing system for Unix.

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Answer 3

etresoft

Level 9

56,692 points

Feb 27, 2011 5:39 PM in response to Aaron d´Europe

I don't have specifics for MacOS X, but often, in other UNIX operating systems, it can be something as random as the first drive to spin up. Those device names are not reliable between restarts.

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Answer 4

Feb 28, 2011 3:55 PM in response to Aaron d´Europe

It can't be the master/slave-config. The small 3 GB drive is manually jumpered as slave.
(Not before I put a jumper-bridge between 2 pins, changing the 3 GB-drive to slave-mode, the G4 was able to boot up. I vaguely remember a knowledge-base article explaining that "Cable select" is originally only used in Mirrored Drive Door-G4s and some older 2002-Quicksilvers.)

What triggered my curiosity was the fact, that even the drive was slave and it was FAT32 formatted, at the first startup it became assigned as "drive0" and my original boot disk became drive1. However since I reformatted the Fujitsu to HFS+ (journalled) it is now and permanently assigned drive1.
The theory that it's just a question which drive boots up quicker, that will become drive0, seems plausible to me. I also assume that sinple DOS-formatted drives are faster online than the more complicated HFS+ formatted ones. This would explain the change in the drive-numbers after reformatting.

But this is just a guess

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