something to keep in mind: system databases cannot be restored from previous versions or servicepacks;(regular databases are no problem)
so say you backed up master, msdb and model in RTM (release to market base version), then upgraded to SP2;
if any of those db's get corrupted, you cannot restore from those previous backups; after an upgrade you need to do a fresh set of backups that match the exact version.
so if model got corrupted, you'd have to get a model from another instance with the same service packs applied (and maybe CU's as well...i'd have to double check on that)
also on bootup, isn't tempdb born as a copy of model?
it might be a pain to track something like that down (especially if you are in an environment with out too many servers!)
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