We got it from our hosting site:
Our monitoring has detected a hardware issue on the node that hosts your VPS. The issue is related to a battery backup on a RAID controller. In order to correct the problem we need to replace the battery, which involves shutting down the node.
The node will be shut down at 11:00 PM (Central US time) on Friday May 30th. We expect the node to be down for no more than 30 minutes.
Unfortunately that is 5 AM my time, so if something goes wrong I may be not aware of problems before I wake up, and I am not an early bird type. But the team at CyberLynk proved to be highly competent in the past, so I don't expect any troubles.