Thomas Olschewski wrote:
> A lvchange -ay /dev/mediaLVM/vol1 did it.

That was going to be my next suggestion...
(beat me to it)

>
> I think problem could be that I work without initrd. When fstab entries are
> mounted, USB devices are not ready. LVM is not active without USB HDDs and
> fstab can't mount the LVM.

Sounds very likely. Any reason for not using initrd?