Locking device nodes to devices

Mark Ovens mark at ukug.uk.freebsd.org
Mon Dec 11 20:00:12 GMT 2006


Hi,

Is there any way to "lock" a device node to a specific physical (SCSI) 
device?

I've got 3 optical drives and a DAT drive in an external enclosure and a 
second DAT drive in another external box. The latter is normally 
switched off (it's a bit noisy) so the DAT in the main external box is sa0.

Tonight, while the second external box was switched on, we had a power 
cut. Once the power came back on I carried on where I left off doing 
some backups but kept getting "Device not configured" errors for sa1 - 
the second DAT drive. Eventually, after reading the output from dmesg(8) 
*carefully* I realized that the devices had been swapped round, i.e. the 
drive I thought was sa1 was now sa0.

OK, I could change the SCSI IDs of all the devices to ensure that the 
first DAT drive is probed first (but is that guaranteed?) but that would 
mean changing /etc/fstab and possibly other things, e.g. scripts.

So, can sa0 be "locked" to the first DAT drive so that, even if the 
second external box is powered up when the computer boots up, the drive 
in the first external box will always be sa0?

Thanks.

Regards,

Mark




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