UUIDs on drives

[ghe]

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Brian McKee wrote:

| What if you have two identical model controllers in your computer?
| Which one gets scanned first is unpredictable by anybody...

The one with the lowest PCI identifier goes first.

| How about redundant iSCSI SAN devices?  What drive letter are you
| going to reserve for them?

Sorry, but I don't know what that is (Steve Jobs is bringing back
SCSI?). But if there are 2 SCSI devices, they'll have different
addresses on the bus.

| What if the first harddrive on the scsi bus doesn't have the OS on it,
| and you remove it?

The installer has told everybody that the drive with the OS is at port
0Xnnnn, SCSI id #m. Or PCI slot #n, SATA channel #m. No problem.

If you pull the one that *does* have the OS, though, you have to put it
back :-) Where it was.

| First how incidentally?

By PCI 'slot', then by port on that device (or SCSI id or the like). But
consistently.

| What happens when a RAID array fails?

Depends on how the array is built. If it's on a RAID card, it'll
(probably) look like one (broken) device to the computer. If it's
software, it'll look like one of <n> broken drives.

If something's broken, though, it's some techie's problem, no mater how
addressing's done.

| How exactly can you tell the difference between a picture frame, an
| MP3 player and a USB stick?  They're probably using the same chipset
| anyways....

Good point. But they're still plugged into port #0 or #35 or something
on the USB chip. There's still an order at the hardware level, even
though it may not mean a lot at the software level.

| Mac doesn't do it by fixed position AFAIK incidentally.  I believe EFI
| scans for all possible bootable drives, then if it finds the one
| that's the same one as it was told to boot from next it will do so,
| otherwise it picks the 'next' one it finds,  and that order can change
| depending on what you plug in when.

That's a reasonable way to handle that error condition: go looking for
something bootable. The machine will at least boot.

| Identifying the file system at the file system level uniquely is the
| only solution I can think of that deals with all this mess of
| different devices that appear at different times and places.

Yes. At the software level. But at boot time, the hardware must be
identifiable uniquely, and repeatably.

Unless you've got a Mac that's smart enough to go looking around for
some useful software...

- --
Glenn English
ghe at slsware.com

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