My server makes full backups every week (and incremental backups daily) to an external FTP server. This FTP server has 12.16 TB free space (the last full backup was 327 GB) and there are no restriction for the FTP user or specific folder. I've tested the FTP username and password and verified that these are correct. There weren't any problem before.

The last time that an full backup was required the server used all available (local) disk space and filled the local disk. After some investigation I found that the backup process has filled up the disk space in the /var/log/plesk/PMM/ folder.
The Plesk settings doesn't allow the backup to be stored locally. I've tried enabling "Start the backup only if your server has the sufficient amount of free disk space (this option may significantly increase the backup time) " but this would not prevent the backup (300+ GB) from filling up the /var/log/plesk/PMM/ folder (with 220 GB free space). I've also disable "Save backups in the server storage if the upload to FTP fails".

Yesterday 219G was available on my server (more than enough for normal daily operations). If the backup process (more than 300G) tries to store the backup in the /var/log/plesk/PMM/ folder it will fill the disk and prevent functions like Databases, Sessions or Plesk from working. I than have to manually intervene by remove the created files in the /var/log/plesk/PMM/ folder. To prevent the backup proces from bricking my system I've created a cronjob that removes all backup files from /var/log/plesk/PMM/ hourly.
Why is the backup process trying to use the local storage instead of the FTP server? Due to this behavior I don't have any recent backups available.

The last time that an full backup was required the server used all available (local) disk space and filled the local disk. After some investigation I found that the backup process has filled up the disk space in the /var/log/plesk/PMM/ folder.
The Plesk settings doesn't allow the backup to be stored locally. I've tried enabling "Start the backup only if your server has the sufficient amount of free disk space (this option may significantly increase the backup time) " but this would not prevent the backup (300+ GB) from filling up the /var/log/plesk/PMM/ folder (with 220 GB free space). I've also disable "Save backups in the server storage if the upload to FTP fails".

Yesterday 219G was available on my server (more than enough for normal daily operations). If the backup process (more than 300G) tries to store the backup in the /var/log/plesk/PMM/ folder it will fill the disk and prevent functions like Databases, Sessions or Plesk from working. I than have to manually intervene by remove the created files in the /var/log/plesk/PMM/ folder. To prevent the backup proces from bricking my system I've created a cronjob that removes all backup files from /var/log/plesk/PMM/ hourly.
Filesystem Size Used Avail Use% Mounted on
/dev/ploop14118p1 591G 342G 219G 61% /
Why is the backup process trying to use the local storage instead of the FTP server? Due to this behavior I don't have any recent backups available.