All of our recent Solaris 10 installs use the ZFS root feature. Hence we use luupgrade to clone off a copy of root, patch that, then activate and boot into the clone. So downtime is just the time needed for the reboot. This part is similar to what Linux people have been seeing for years.
What is improved for us though, is the ability to "boot -L" and "boot -Z" to boot into previous boot environments if there is some issue with a new patch. We do not need to untangle which patch caused a problem in order to return to production We actually use a local script called "patchbe" which wraps some error-checking and other functions around luupgrade capability. We check for pool integrity, run JASS on the clone, etc. Switching to ZFS root and patchbe has taken out nearly all of the worries of monthly patching.
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