Re: direct reads and writes on Solaris
- From: Dan Norris <dannorris@xxxxxxxxxxxxx>
- To: ukja.dion@xxxxxxxxx, Oracle L <oracle-l@xxxxxxxxxxxxx>
- Date: Thu, 24 Jan 2008 16:10:56 -0800 (PST)
Thanks, looks like that confirms my theory below. (Not sure how I didn't find
those references myself--sorry.) I then have one related question.
We did some specific testing where we used a crude method to test I/O
(specifically, write) performance. The test was this:
timex dd if=/dev/zero of=<device> bs=1024k count=2048
For the <device> we tried many different things. The interesting part (and
here's where I'd like some input) is that the results for testing the same
device via buffered (block) devices was much, much slower than the result for
the unbuffered (char) device. All things equal, here are some sample tests:
/dev/vx/dsk/testdg/test
real 25.12
usr 0.02
sys 24.94
/dev/vx/rdsk/testdg/test
real 10.35
usr 0.01
sys 1.55
So, basically, it took more than 2x as long to do the dd to the buffered device
as compared to the unbuffered device. I was sort of expecting that writes to
the buffered device would be possibly a little faster or maybe about equal. I
never expected to have such a big delta and I also didn't expect that so much
system time would be spent just writing to a buffered device.
Any of you I/O gurus see anything interesting in these results? Are the testing
methods even valid? My conclusion is that since we're likely doing buffered I/O
now (since we're not doing directIO), that if we switched to doing directIO
(which is unbuffered by definition), that we'd see considerable performance
gain--at least for writes (since my test was only for writes). I would presume
that reads might be a similar ratio though.
Dan
----- Original Message ----
From: Ukja.dion <ukja.dion@xxxxxxxxx>
To: dannorris@xxxxxxxxxxxxx; Oracle L <oracle-l@xxxxxxxxxxxxx>
Sent: Thursday, January 24, 2008 5:55:18 PM
Subject: RE: direct reads and writes on Solaris
<!--
_filtered {font-family:"Cambria Math";panose-1:2 4 5 3 5 4 6 3 2 4;}
_filtered {font-family:"Malgun Gothic";panose-1:2 11 5 3 2 0 0 2 0 4;}
_filtered {font-family:"Malgun Gothic";panose-1:2 11 5 3 2 0 0 2 0 4;}
_filtered {font-family:Verdana;panose-1:2 11 6 4 3 5 4 4 2 4;}
_filtered {font-family:Tahoma;panose-1:2 11 6 4 3 5 4 4 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;margin-bottom:.0001pt;font-size:12.0pt;font-family:"Times
New Roman", "serif";}
a:link, span.MsoHyperlink
{color:blue;text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{color:purple;text-decoration:underline;}
span.EmailStyle17
{font-family:"Verdana",
"sans-serif";color:windowtext;font-weight:normal;font-style:normal;text-decoration:none
none;}
.MsoChpDefault
{}
_filtered {margin:3.0cm 72.0pt 72.0pt 72.0pt;}
div.Section1
{}
-->
Visit
following URLs
http://www.solarisinternals.com/wiki/index.php/Direct_I/O
http://www.ixora.com.au/notes/filesystemio_options.htm
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Dan Norris
Sent: Friday, January 25, 2008 7:14 AM
To: Oracle L
Subject: direct reads and writes on Solaris
Can
someone help me interpret this set of data correctly?
The (vxfs) filesystem is mounted with these options:
/db51 on /dev/vx/dsk/oracledg/db18
read/write/setuid/mincache=direct/delaylog/largefiles/ioerror=mwdisable/dev=3ac36c1
This is 9.2.0.8 on Solaris 9 (V490, Generic_122300-07) with VxFS 4.1.
I have the following line in a truss of a dedicated server process:
open("/db51/oradata/tccrt1/member_questions_d01.dbf", O_RDWR|O_DSYNC)
= 9
I also have the following settings in the DB:
NAME
TYPE VALUE
------------------------------------ ----------- ------------------------------
disk_asynch_io
boolean TRUE
filesystemio_options
string ASYNCH
The question(s):
I was expecting to see O_DIRECT in there somehow, but I'm thinking that maybe
that's just on Linux, not Solaris. I don't see O_DIRECT listed in the open(2)
manual page. I am also wondering if filesystemio_options needs to be
"setall" instead of the current setting of "ASYNCH" in
order to achieve directIO. Or, am I looking at the wrong thing to determine if
directIO is enabled?
Thanks in advance!
Dan
Other related posts:
