Simen Timian Thoresen wrote:
So - with the LV unmounted, I power my USB-device down, and then back up;
I believe your problem is you didn't deactivate the logical volume, and export the volume group before disconnecting.
lvchange -a n <path to lvm> vgexport -a (don't worry it will only export groups that are ready to be exported)
Now you can safely power the device down(provided the VG was successfully exported, all logical volumes must be unmounted and deactivated before it will succeed).
when you power it back up run
pvscan vgimport -a lvchange -a y <path to lvm>
LVM is very useful for volumes that change device names, but you must use it properly otherwise bad things will happen as you saw.
If you want to have USB mount automatically it may be better to put a label on the file system, at least in Debian(don't have a CentOS system with a USB disk handy here) the volume is mounted as /media/<disk label> if there is a disk label. You can use the e2label command to label the device. I'd expect CentOS to likely behave similarly to debian in this respect.
nate