Let me see.
I plug in USB camera. Shos up at /dev/sda. I add USB drive. Shows up at /dev/sdb.
Tomorrow I plug in USB drive. Shows up at /dev/sda I plug in USB camera. Shows up at /dev/sdb.
What if I have _two_ USB drives (I do - one for carrying stuff, one for backups)?.
A filesystem label would help overcome the confusion.
Didn't I read somewhere that sata drives are hdx with 2.4 kernels, sdx with 2.6?.
This is correct. SATA drives are sd* in 2.6. And yeah, sd* devices change names when you connect/disconnect/replace them. Something I always considered Linuxs' weak point.
Anyhow, as I already wrote couple of times, all this confusion could have been avoided if Linux by any chance implemented uniq device names based on hardware properties. Either the way Solaris does it (not ideal, but light years better than current Linux mess), or using something smarter.
This way, your /boot partition would be something like /dev/dsk/c0t0d0s0 (I won't go into describing Solaris /devices directory hierarchy, something most users dread cd-ing into, only the symbolic links in /dev directory). Transleated this device name is:
- s0: first partition
- d0: on first LUN (if it is multi-lun SCSI device, always zero for preatty much everything else)
- t0: on disk with ID 0 (SCSI ID for SCSI, 0 for master IDE drive, 1 for slave IDE drive, WWN for fibre channel, or something else that is uniq for other bus types)
- c0: on controller number zero (system remembers what controllers you had, so numbers do not change when you add/remove controllers).
Now let say you had SCSI controller in the box, and it was assigned controller ID 1 (c1). If you remove it from the system, your USB devices will still be c2, and your SATA controller would still be c0. If you connect new controller (SCSI, SATA, old ATA, USB, whatever), it will be assigned as c3 (not now unused c1). If you reconnect your SCSI controller back, it will reappear as c1 (so all devices connected to it will reuse their old device names).
Try that on Linux. Each time you connect or disconnect something, all your /dev/sd* devices will shift. On Solaris, nothing shifts. All device names stay the same as if their names were carved in the rock.
Your USB camera would than be /dev/dsk/c2tXXXXd0sY, where c2 is your USB controller, and XXXX is some uniq ID stored in your camera hardware. Your USB drive would have different uniq ID. No matter in which order you connect them, they are always assigned same device names. You don't need labels on them. I don't know much about USB internals, but I guess there's probably something in each USB devices to make more or less uniq device name.
If you have shell access to Solaris box (either sparc or intel), check out file /etc/path_to_inst (yeah, the one that begins with comment "Caution! This file contains critical kernel state"). It is the file where Solaris keeps record of all devices that were ever connected to the system, so that if they get reconnected they get their original device name. It is kind of your system's hardware past and present (well, Solaris isn't smart enough to guess the future, but that part might be added to Linux implementation ;-) ). If you connect new device (while old one is not connected), it will get new name (old one is still reserved if you decide to reconnect old device).
Actually, on Solaris, if you move controller from one PCI slot to another, system will detect that and treat it as new controller (new controller ID). Sometimes this is neat, sometimes it is pain in the butt. But nothing is ideal ;-)
Theoretically, something like this could be added from user space on Linux systems (basically, by expanding and developing on the current idea of linking /dev/cdrom and /dev/floppy to appropriate device names). But it would be light years simpler and more stable if Linux kernel was changed to cooperate in this.
-- Aleksandar Milivojevic <amilivojevic@xxxxxx> Pollard Banknote Limited Systems Administrator 1499 Buffalo Place Tel: (204) 474-2323 ext 276 Winnipeg, MB R3T 1L7
