On Dec 16, 2009, at 6:54 PM, Bob Friesenhahn wrote:
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
I just threw that together, and it doesn't do anything clever like
identify sequential writes. Is there an actual problem that we
can solve by looking at the alignment? If so, maybe we can
do better...
% iopattern
I modified iopattern so you can separate reads from writes.
I find that seeing them mixed is of little use, and very confusing :-)
http://www.richardelling.com/Home/scripts-and-programs-1/iopattern
-- richard
%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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