I am planning on doing some maintenance at the co-lo facility tonight that will involve rebooting three of the host servers. These are the machines that have your /home directories and /var/spool/mail mail spools, as well as various virtual machines.
The last time I did this we were down for several hours. I have come to a good understanding of what caused the issues last time so they can be avoided this time. I expect a downtime of about 1/2 hour for the server that hosts /home directories and about 10-15 minutes for the others.
The reason for these reboots is to load a 4.8 Linux kernel. There was substantial work done to NFS in version 4.8 that improves performance by correcting a few sections of slow critical code and by using more aggressive caching. Since our whole service is heavily dependent upon NFS to mount file systems remotely from one machine to another, this should improve the overall performance of our network, Mail, Web, shell serves, all should run faster after this reboot.