I have done the same solution and it works nicely with LABEL=STORAGE and naming different USB sticks to STORAGE
but when I unplug a USB stick and reinsert it I get input output errors.
If i reboot the machine it works nicely again.
This is after I reinserted a USB drive
----snap dmesg output
[314008.563247] usb-storage 1-1.2:1.0: USB Mass Storage device detected
[314008.595727] scsi host6: usb-storage 1-1.2:1.0
[314010.535236] scsi 6:0:0:0: Direct-Access SMI USB DISK 1100 PQ: 0 ANSI: 4
[314010.547511] sd 6:0:0:0: [sda] 31211520 512-byte logical blocks: (16.0 GB/14.9 GiB)
[314010.548022] sd 6:0:0:0: Attached scsi generic sg0 type 0
[314010.548968] sd 6:0:0:0: [sda] Write Protect is off
[314010.549013] sd 6:0:0:0: [sda] Mode Sense: 43 00 00 00
[314010.550391] sd 6:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn’t support DPO or FUA
[314010.562474] sda: sda1
[314010.569243] sd 6:0:0:0: [sda] Attached SCSI removable disk
An ls works nicely so the mount seems to be working
root@88110ad:/usr/src/app# ls /mnt/storage/
Also syctemctl likes it
root@88110ad:/usr/src/app# systemctl status mnt-storage.mount
● mnt-storage.mount - External USB stick storage
Loaded: loaded (/etc/systemd/system/mnt-storage.mount; enabled)
Active: active (mounted) since Fri 2017-08-11 12:07:10 UTC; 1h 9min ago
Process: 44 ExecMount=/bin/mount -n LABEL=STORAGE /mnt/storage -t vfat -o rw (code=exited, status=0/SUCCESS)
Aug 11 12:07:10 88110ad systemd: Mounted External USB stick storage.
Warning: Journal has been rotated since unit was started. Log output is incomplete or unavailable.
But when trying to write it fails
root@88110ad:/usr/src/app# touch /mnt/storage/test.txt
touch: cannot touch ‘/mnt/storage/test.txt’: Input/output error