Which device is using this logical volume?
Use lsof(8):
# lsof /dev/vg_service1/lv_home
I don't have access to a Linux box at this very moment to verify its output, but here's what it looks like on my Mac:
# lsof /dev/disk1 | head
COMMAND PID USER FD TYPE DEVICE SIZE/OFF NODE NAME
launchd 1 root cwd DIR 14,4 1564 2 /
launchd 1 root txt REG 14,4 415248 7402611 /sbin/launchd
launchd 1 root txt REG 14,4 59504 7399166 /usr/lib/libauditd.0.dylib
launchd 1 root txt REG 14,4 599232 7402371 /usr/lib/dyld
launchd 1 root txt REG 14,4 289054720 8865364 /private/var/db/dyld/dyld_shared_cache_x86_64
launchd 1 root 20r DIR 14,4 170 7402529 /private/var/tmp
launchd 1 root 24r REG 14,4 0 9885226 /private/var/run/socketfilterfw.launchd
launchd 1 root 25r DIR 14,4 2040 7393527 /private/var/db
You should see something similar on your system.
It turned out that the logical volume was itself part of a volume group. It didn't show up in /proc/mounts or in the output of lsof. The only way I was able to discover this was through the "pvdisplay" command, where it appeared as a physical volume:
# pvdisplay
...
--- Physical volume ---
PV Name /dev/vg_service1/lv_home
VG Name nova-volumes
PV Size 179.91 GiB / not usable 4.00 MiB
...