On 2016-09-23 11:49, Edgar Fuß wrote:
The whole point of tagged queueing is to let you *not* set [the write cache] bit in the mode pages and still get good performance.I don't get that. My understanding was that TCQ allowed the drive to re-order commands within the bounds described by the tags. With the write cache disabled, all write commands must hit stable storage before being reported completed. So what's the point of tagging with cacheing disabled?
Totally independent of any caching - disk I/O performance can be greatly improved by reordering operations to minimize disk head movement. Most of disk I/O times are head movements. I'd guess that makes up about 90% of the time.
Johnny
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