I have a crontab script that backup a specific folder in a external drive,

I have a script daily_backup.sh that was called in my crontab

this is my crontab script.
30 2 * * 1-5 /home/admin/daily_backup.sh


this is my daily_backup.sh

rm -fR /backupdrive/data

cp -apv /project/data /backupdrive

note:
/backupdrive is my external vfat drive

/project/data is my data from my linux.

there are existing files in my external drive so when rm -fR is process it deletes first the files then re-copy it.

when crontab is process, the rm -fR begins but when the cp -apv its stop and only one folder from the data is copied.

and by the way when I tried to manually run the daily_backup.sh its ok.
maybe theres something problem in copying to the external drive