We tested HD Tach with the benchmark's full variable zone size setting.
The Caviar Black's areal density advantage over the Barracuda XT doesn't amount to more than 1MB/s in HD Tach's sustained read speed test. It's good for up to 7MB/s in the write speed test, though. The Barracuda doesn't read any quicker when connected to the Marvell controller, but it's a good 2MB/s slower in the write speed test.
We'd expected HD Tach's burst speed test to be able to tell us whether the Barracuda XT's cache is quick enough to take advantage of a 6Gbps link. Unfortunately, the Marvell controller evidently treats system memory as the drive cache for this test, which is why we're seeing the Marvell solution churn out more than six times the peak bandwidth available in a 600MB/s Serial ATA link. The Caviar Black achieves similarly impressive burst speeds when connected to the Marvell, though.
Perhaps more relevant are the burst speed results from our P55 configs. With that controller, the Barracuda XT pulls up 24MB/s short of the Caviar Black.
Ouch. Despite the fact that the Barracuda XT has the same 7,200-RPM spindle speed as the Caviar Black, the Seagate drive's random access time is more than 4.5 milliseconds slower. A handful of milliseconds may not sound like much, but in a modern PC, that's a long time. We're also talking about a 23% difference, which is one of the biggest margins we've seen today.
As one might expect, there isn't much difference in CPU utilization between the drives and controllers. Ain't pseudo-eight-core processors grand?