Jeff Garzik wrote:
TCQ-on-write for ATA disks is yummy because you don't really know what the heck the ATA disk is writing at the present time. By the time the Linux disk scheduler gets around to deciding it has a nicely merged and scheduled set of requests, it may be totally wrong for the disk's IO scheduler. TCQ gives the disk a lot more power when the disk integrates writes into its internal IO scheduling.
Does TCQ-on-write allow you to do ordered write commits, as with barriers,
but without needing full cache flushes, and still get good performance?