We will be off line, the entire network, for up to about half an hour, starting around 2AM Sunday morning, to replace a failing drive in the machine which is also acting as a router at present.  This drive is part of a RAID array so all data is duplicated and none will be lost.  If things go smoothly, it could be as short as 15 minutes, if not then maybe half hour or slightly longer.

The big unknown is that sometimes when software RAID comes up in degraded mode, which it will do initially until the new drive is pumped up, sometimes systemd will hang necessitating going through emergency mode and bringing things up by hand.  In my experience this is about 30% of the time.  It will take usually about 6-8 hours for the system to sync a new 4TB drive but the system can operate while this is in progress it just sometimes Poetteringware adds some challenges.