The iscsi-shutdown.service is the one responsible for logging out
iscsi sessions so blk-availability.service (running the blkdeactivate
script) should be run before that on shutdown (so we need to use
After=iscsi-shutdown.service because "After" relates to starting
the service and the opposite order is automatically applied on
stopping the service at shutdown).
git://sourceware.org / lvm2.git / commit