* all is usually cached by udev in /dev/disk/by-* and libblkid
is able to use these symlinks
* boot persistent cache is attractive for very small subset of
Linux machines (and they already need extra udev tunning otherwise
udev will probe all block devices during boot)
* the default is possible to override in /etc/blkid.conf
The systems without /run directory will not be affected by this
change.