Postfix and “noatime” Mounts
Never – ever – mount a filesystem Postfix uses with the noatime option. If you have fast_flush_domains enabled (which is is, by default) and you have a lot of deferred mail for which you’re the relay host, it will cause mail delays because the flush service uses atime to decide when it should refresh the fast flush files. It does this by requesting delivery of every queue id in the file. If atimes are disabled, it will keep flushing the entire deferred queue over and over, resulting in horrible mail delivery performance.
Leave atime enabled (the default on mount) and get faster disks or hardware RAID with battery backed cache if you need a performance boost. Switching to a filesystem like XFS over ext3 also helps if you’re shuffling a lot of files around. But never mount as noatime – it’s never worth it.