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0f7b58d
(Get the code!)
Since my last comment, I have done some more testing. While performance is generally much better than it was a year ago, it still isn't quite as fast as it should be on two of my drives, and these drives don't appear to be running in any UDMA mode. The other one seems to perform a bit better, and has udma5 enabled. Here's the relevant output of hdparm -i and hdparm -tT on each of my three drives (the full output is attached):
# Maxtor 80GB SATA
UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5
Timing buffered disk reads: 170 MB in 3.01 seconds = 56.39 MB/sec
# Seagate 80GB SATA
UDMA modes: udma0 udma1 udma2 udma3 udma4 *udma5
Timing buffered disk reads: 224 MB in 3.01 seconds = 74.42 MB/sec
# Western Digital 500GB SATA
UDMA modes: udma0 udma1 udma2 udma3 udma4 udma5
Timing buffered disk reads: 206 MB in 3.02 seconds = 68.15 MB/sec
Copying a 700MB ISO image between each of these drives takes between 11 and 20 seconds, with the mean average being about 15 seconds; the faster the transfer, the higher the CPU usage (up to 30% in some cases, much higher than I would expect considering DMA is supposed to be in use). I have attached details of this test as well (9 copy operations in all), in case this is of any use.
Of course, I don't really know what speeds I'm supposed to get on these drives - I have never paid much attention to copy speed until this problem occured. It's possible that these speeds are normal (they're certainly quick enough that this isn't as big an issue as it was), though the fact that UDMA still seems to be disabled on two drives makes me think something is still not working as it should.