Timo Sirainen put forth on 1/31/2011 9:43 PM:
O_DIRECT is completely useless for just about every application there is. It was written for Oracle, and I doubt there are many applications outside (SQL) databases that use it at all.
It's not suitable at all for mail. I didn't imply that. I merely mentioned it as it is one of the calls other than fsync that guarantees the data hit the disk. Since we're discussing it, it is used outside databases, heavily in HPC and the scientific community, one example being satellite data feed capture, where it doesn't make sense to push multiple gigabytes per second through the buffer cache before hitting the disks.
Ted also thinks everyone should be using SQL(ite) database rather than filesystems directly. Many people don't agree.
I don't claim to have read all of Ted's writings so I can't really comment on this. I originally quoted his blog post because of his comments on fsync and the behavior of all modern filesystem with regard to data resiliency after power loss in response to a comment Frank made, IIRC. Dovecot does fsyncs by default so this doesn't apply obviously.
Again, sorry for the OT noise.
-- Stan