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SubjectRe: Why is NCQ enabled by default by libata? (2.6.20)
Here's some more data.

6x ST3400832AS (Seagate 7200.8) 400 GB drives.
3x SiI3232 PCIe SATA controllers
2.2 GHz Athlon 64, 1024k cache (3700+), 2 GB RAM
Linux 2.6.20.4, 64-bit kernel

Tested able to sustain reads at 60 MB/sec/drive simultaneously.

RAID-10 is across 6 drives, first part of drive.
RAID-5 most of the drive, so depending on allocation policies,
may be a bit slower.

The test sequence actually was:
1) raid5ncq
2) raid5noncq
3) raid10noncq
4) raid10ncq
5) raid5ncq
6) raid5noncq
but I rearranged things to make it easier to compare.

Note that NCQ makes writes faster (oh... I have write cacheing turned off;
perhaps I should turn it on and do another round), but no-NCQ seems to have
a read advantage. %$%@#$@#ing bonnie++ overflows and won't print file
read times; I haven't bothered to fix that yet.

NCQ seems to have a pretty significant effect on the file operations,
especially deletes.

Update: added
7) wcache5noncq - RAID 5 with no NCQ but write cache enabled
8) wcache5ncq - RAID 5 with NCQ and write cache enabled


RAID=5, NCQ
Version 1.03 ------Sequential Output------ --Sequential Input- --Random-
-Per Chr- --Block-- -Rewrite- -Per Chr- --Block-- --Seeks--
Machine Size K/sec %CP K/sec %CP K/sec %CP K/sec %CP K/sec %CP /sec %CP
raid5ncq 7952M 31688 53 34760 10 25327 4 57908 86 167680 13 292.2 0
raid5ncq 7952M 30357 50 34154 10 24876 4 59692 89 165663 13 285.6 0
raid5noncq 7952M 29015 48 31627 9 24263 4 61154 91 185389 14 286.6 0
raid5noncq 7952M 28447 47 31163 9 23306 4 60456 89 198624 15 293.4 0
wcache5ncq 7952M 32433 54 35413 10 26139 4 59898 89 168032 13 303.6 0
wcache5noncq 7952M 31768 53 34597 10 25849 4 61049 90 193351 14 304.8 0
raid10ncq 7952M 54043 89 110804 32 48859 9 58809 87 142140 12 363.8 0
raid10noncq 7952M 48912 81 68428 21 38906 7 57824 87 146030 12 358.2 0
------Sequential Create------ --------Random Create--------
-Create-- --Read--- -Delete-- -Create-- --Read--- -Delete--
files:max:min /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP /sec %CP
16:100000:16/64 1351 25 +++++ +++ 941 3 2887 42 31526 96 382 1
16:100000:16/64 1400 18 +++++ +++ 386 1 4959 69 32118 95 570 2
16:100000:16/64 636 8 +++++ +++ 176 0 1649 23 +++++ +++ 245 1
16:100000:16/64 715 12 +++++ +++ 164 0 156 2 11023 32 2161 8
16:100000:16/64 1291 26 +++++ +++ 2778 10 2424 33 31127 93 483 2
16:100000:16/64 1236 26 +++++ +++ 840 3 2519 37 30366 91 445 2
16:100000:16/64 1714 37 +++++ +++ 1652 6 789 11 4700 14 12264 48
16:100000:16/64 634 11 +++++ +++ 1035 3 338 4 +++++ +++ 1349 5
raid5ncq,7952M,31688,53,34760,10,25327,4,57908,86,167680,13,292.2,0,16:100000:16/64,1351,25,+++++,+++,941,3,2887,42,31526,96,382,1
raid5ncq,7952M,30357,50,34154,10,24876,4,59692,89,165663,13,285.6,0,16:100000:16/64,1400,18,+++++,+++,386,1,4959,69,32118,95,570,2
raid5noncq,7952M,29015,48,31627,9,24263,4,61154,91,185389,14,286.6,0,16:100000:16/64,636,8,+++++,+++,176,0,1649,23,+++++,+++,245,1
raid5noncq,7952M,28447,47,31163,9,23306,4,60456,89,198624,15,293.4,0,16:100000:16/64,715,12,+++++,+++,164,0,156,2,11023,32,2161,8
wcache5ncq,7952M,32433,54,35413,10,26139,4,59898,89,168032,13,303.6,0,16:100000:16/64,1291,26,+++++,+++,2778,10,2424,33,31127,93,483,2
wcache5noncq,7952M,31768,53,34597,10,25849,4,61049,90,193351,14,304.8,0,16:100000:16/64,1236,26,+++++,+++,840,3,2519,37,30366,91,445,2
raid10ncq,7952M,54043,89,110804,32,48859,9,58809,87,142140,12,363.8,0,16:100000:16/64,1714,37,+++++,+++,1652,6,789,11,4700,14,12264,48
raid10noncq,7952M,48912,81,68428,21,38906,7,57824,87,146030,12,358.2,0,16:100000:16/64,634,11,+++++,+++,1035,3,338,4,+++++,+++,1349,5
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