I don't keep up on enterprise Linux stuff much but after reading this it concerns me that Linux seems to have better in-place upgrade support than most of Cisco's big iron stuff I've worked with. The 10000 series routers I presently work with only recently got support for in-place upgrades and it has a list of caveats a mile long. From a network architecture standpoint you can't always (affordably) design around downtime but at least your servers can stay up while your network is done now.
