btrfs fi show -d
(/dev/mapper/vg1000-lv)

syno_poweroff_task -d

(or: umount /volume1)
(or2: umount /volume1 -f -k)

Check to see if all us unmounted:
df -h

mdadm --stop /dev/vg1000/lv

btrfsck /dev/vg1000/lv

btrfs check --repair /dev/vg1000/lv

btrfs rescue super-recover -v /dev/vg1000/lv

vgchange -ay

e2fsck -nvf -C 0 /dev/vg1000/lv

fsck.ext4 -pvf -C 0 /dev/vg1000/lv

(or: e2fsck -pvf -C 0 /dev/vg1000/lv -C O)
(do not do this: -C fd)