Because there's no "normal" way to create a Data Scrubbing scheduled task, we need to this the hard way ;-) although it's not that hard, however it takes a bit more than just clicking some wizard, below you will find all the steps required to create a scheduled data scrubbing task.
Login to DSM (example; https://your-nas:5001/)
Open Control Panel and go to Terminal & SNMP, and make sure that Enabled SSH Service is checked (enabled)
Use a terminal emulator like Terinal/Console for OSX/Linux of Putty for the Windows folks
ssh admin@your-nas and open a new session as root
sudo su -
wget -P /volume1/ https://raw.githubusercontent.com/remonlam/synology-data-scrubbing/master/start_data_scrubbing.sh
Go to the location where the script has been stored (in this example it's /volume1) cd /volume1 ls -lh
It should show something like this; root@nas:/volume1# ls -lh -rwxr-xr-x 1 root root 402 Oct 9 15:54 start_data_scrubbing.sh
It it's not executable just run; chmod 755 start_data_scrubbing.sh
Go back to the DSM (web console).
Open Control Panel and go to Task Scheduler
Next, go to "Create" --> "Scheduled Taks" --> "User-defined script".
Enter a name (for example; Data Scrubbing on node NAS) and make sure it runs as root!
According Synology it's best to run Data Scrubbing once every month, so create a schedule that it run's every month.
Optional is to get an email when the script has run. If you want this enter your mail address.
The last step is to fill in the location of the script that have been copied earlier. In my example it's /storage1/start_data_scrubbing.sh md2 and click on OK to create the task.
Check if the tasks has been created.
To check if everything is working select the task and click on "Run".
In DSM (web console) open the Storage Manager
And select either Volumes or Disk Group and check if it's there are Parity Check's running
NOTE: Depending on the amount of data stored on the disk and the total size of the disks this can take some time to complete...
Because we don't need SSH to be open anymore it's security wise better to disable it. In DSM (web console) open the Control Panel
Uncheck "Enable SSH Service" and click on Apply, SSH is no disabled!