Thanks for the information Richard!
The output of running arcstat.pl is included below. A potentially
interesting thing I see is that the "Prefetch miss percentage" is
100% during this test. I would have thought that a large sequential
read test would be an easy case for prefetch prediction.
When I first start the test and am seeing a 100Mbytes/sec
read rate, arcstat output is:
Time read miss miss% dmis dm% pmis pm% mmis mm% arcsz c
10:29:22 685 374 54 9 2 365 100 7 2 51M 490M
10:29:23 2K 855 37 7 0 848 100 7 0 163M 490M
10:29:24 2K 774 33 6 0 768 100 6 0 264M 490M
10:29:25 3K 1K 33 8 0 1K 100 8 0 398M 490M
10:29:26 2K 774 30 6 0 768 100 6 0 413M 412M
10:29:27 2K 1K 34 8 0 1K 100 8 0 413M 412M
10:29:28 2K 774 35 6 0 768 100 6 0 413M 412M
10:29:29 2K 774 34 6 0 768 100 6 0 413M 412M
10:29:30 2K 774 36 6 0 768 100 6 0 413M 412M
10:29:31 2K 774 35 6 0 768 100 6 0 413M 412M
13 minutes later after the test has run about 30 times (and
still going) and the read rate has dropped to 50 Mbytes/sec
the arcstat output is:
Time read miss miss% dmis dm% pmis pm% mmis mm% arcsz c
10:42:58 1K 523 40 11 1 512 100 4 0 397M 397M
10:42:59 761 266 34 10 1 256 100 2 0 397M 397M
10:43:00 1K 525 41 13 1 512 100 4 0 397M 397M
10:43:01 1K 464 40 15 2 449 100 4 0 397M 397M
10:43:02 932 331 35 12 1 319 100 4 1 397M 397M
10:43:03 1K 534 41 19 2 515 99 8 1 397M 397M
10:43:04 770 266 34 10 1 256 100 2 0 397M 397M
10:43:05 1K 525 41 13 1 512 100 4 0 397M 397M
10:43:06 777 267 34 11 2 256 100 3 1 397M 397M
10:43:08 1K 533 41 18 2 515 99 7 1 397M 397M
Given the information above, is it still likely this degradation
would not occur on a faster machine with more memory?
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