Simple script to create a sensor for PRTG by Paessler which uses the output of btrfs dev stats to show the health of your Btrfs volume.
Sensor tested on DS 918+ with DSM 6.2.4-25556 and 7.0-41890
Be sure you have set correct logon values for SSH in your device.
I personally use "Login via private key" with an user especially for monitoring which also may use sudo for this script without a password.
HINT: Since DSM 6.2.2 for SSH access the user has to be member of the local Administrators group on your Synology NAS.
Place the script to /var/prtg/scriptsxml on your Synology NAS and make it executable. (You may have to create this directory structure because PRTG expects the script here.)
wget https://raw.githubusercontent.com/WAdama/nas_btrfs_stats/master/nas_btrfs_stats.sh
chmod +x nas_btrfs_stats.sh
On your PRTG system place the file prtg.standardlookups.nas.btrfsstats.ovl in INSTALLDIR\PRTG Network Monitor\lookups\custom and refresh it under System Administration / Administrative Tools
In PRTG create under your device which represents your Synology a SSH custom advanced senor.
Choose under "Script" this script and enter under "Parameters" the name of the volume you want to monitor: e.g. volume1.
This sensor will go to warning if one or more value show one or more errors.
