Mechanism for assigning SCSI device names

[dilbert]

Hi all,

I am working on an embedded Linux system and want to get a clue what I have done wrong.

I have a box with an internal and an external harddrive.

Both drives are formatted with ext3 and the internal drive is sda (i.e. sda1, ..., sda4) and the external drive is sdb (i.e. sdb1, sdb2).

The Linux version in this box is 2.6. and removing the external Hard drive and inserting it again always gives sdb. The same way behaves a Feodara Red Hat PC (also 2.6.).

Adding new features, I managed to break this. With my software, when I remove the external hard drive, being sdb, I am getting sdc when I insert it again.

I thought, this is because the external hard drive may have not been unmounted before pulled out but unmounting it manually on the command line doesn't help either.

Any thoughts?

[Jonathan183]

What does mount and cat /etc/mtab report?
Any clues from dmesg?

uuid might work for you instead ...

[dilbert]

What does mount and cat /etc/mtab report?

Well, the embedded version of mount in that box might have been somewhat misleading as after "umount /dev/sdb", manually executed on the command line, I got no error message and the mount point disappeared when I called "mount".

I found the error and it was a missing close(device) statement.

When I read the partition table from the external hard drive, I opened the device but didn't close it.

Pulling out the USB cable from the harddrive, the "umount" command in the disconnecting software couldn't succeed but I saw no error message.
As "umount" failed, /dev/sdb couldn't be released.
Hotplug couldn't re-use sdb and needed to assign sdc instead.

So, there wasn't anything mysterious with hotplug, no hidden "mechanism", it was simply not freeing the device.