On Wed, 16 Dec 2009, Richard Elling wrote:
the same way. A quick dtrace script would show how writes are
aligned to the partition boundaries, but the partition alignment is
left as an exercise for the implementer. -- richard
With 128K reads and writes, not very much apparent alignment in my
pool's writes:
% /usr/sbin/dtrace -Cs aligned.d
Press ^C when done sampling^C
aligned=13014
nonaligned=71464
% iopattern
%RAN %SEQ COUNT MIN MAX AVG KR KW
30 70 592 2560 131072 130744 75586 0
30 70 617 65536 131072 130753 78784 0
30 70 624 65536 131072 130966 79808 0
12 88 2948 512 131072 125161 36224 324105
7 93 6200 3584 131072 130075 0 918510
27 73 1969 512 131072 111426 49216 165040
27 73 633 65536 131072 130657 80768 0
27 73 618 65536 131072 130859 78976 0
25 75 600 65536 131072 130744 76608 0
23 77 606 65536 131072 130963 77504 0
25 75 521 65536 131072 130694 66496 0
7 93 6149 3584 131072 129810 256 779241
13 87 4193 512 131072 124308 10291 498719
26 74 579 2560 131072 130850 73986 0
29 71 609 65536 131072 130533 77632 0
25 75 591 65536 131072 130961 75584 0
25 75 648 65536 131072 130768 82752 0
25 75 603 65536 131072 130963 77120 0
11 89 3278 2048 131072 127439 33280 374677
4 96 6219 3584 131072 129941 0 789167
The percentage of writes which are sequential while reading is
essentially blocked is quite impressive.
Bob
--
Bob Friesenhahn
bfrie...@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/
GraphicsMagick Maintainer, http://www.GraphicsMagick.org/
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