Offering 100% uptime is always our goal, however when it came to critical kernel updates to fix security issues we have no choice but to reboot servers. However, thanks to Ksplice there is now a solution.
Keeping up to date with kernel updates is extremely important and often fixes important security holes. In 2009 there were 16 released, each requires a reboot which takes around 15 minutes to complete. This means there would have been a total of 4 hours downtime just to update the kernel. Ksplice allows us to perform these updates without rebooting and without any impact on performance.
The other advantage is that we can apply patches instantly. We no longer need to plan ahead and give a few days notice of an impending reboot, during this time the server may be open to an exploit causing obvious security problems.