It is impossible to change the diskspace limit for a ploop container on Parallels Cloud Server (PCS) 6.0 (build 1793 and higher) via the Parallels Virtual Automation (PVA) web interface. The corresponding task completes successfully in PVA, but disk space is not increased inside the container.
The issue also occurs wheh setting disk space via the PVA XML API, e.g. for containers managed by Parallels Business Automation - Standard (PBA-S).
This issue is recognized as a product issue with the internal ID PSBM-25118:
vzctl --applyconfig command does not apply diskspace parameter on ploop containers.
The issue has been fixed since Parallels Cloud Server 6.0 Update 6
Install all pending PCS updates and reboot into the latest kernel. In case updates installation was postponed, the workaround is to change the disk space via the CLI backend:
# vzctl set $CTID --save --diskspace 20G