I will be rebooting some servers and taking others down to image them tonight. The reboots are necessary to load a new kernel. Imaging is necessary to have current backups in the event of a machine failure or corruption.
Servers that need to be rebooted include all the host machines so everything will be unavailable for a brief period during this interval but not everything at the same time.
Most outages will be brief (less than ten minutes) but the mail client server will need about a half hour of downtime to image it.