Hi, there!
This article describes how to deal with the problem that hard disk offline and no recording.
Problem Description
Hard disk offline and no recording

Product: VCN540
Problem Analysis
Asking to check the indicators of these hard disks in green lights.

After pulling the offline hard disk and then pushing them again, the issue has been resolved.
Solution
After pulling the offline hard disk and then pushing them again, the issue has been resolved
Thanks for reading!