DBMS_RESOURCE_MANAGER.CALIBRATE_IO
572177Feb 28 2008 — edited Feb 28 2008I was wondering if anyone had any experience, real world preferred, with this 11g procedure.
The inputs to this are:
num_physical_disks: defined by oracle as Approximate number of physical disks
latency defined as Maximum tolerable latency in milliseconds for database block-sized !O requests Max of 100
What is meant by physical, if I have 5 platters but they are stripped etc into one LVM is that 1 or 5?
What value should be used for latency?
Since this returns values to the dba_rsrc_io_calibrate table greater than the value specified forncy, in some cases, for the latency column in that table. What is that setting actually doing?
example, I ran dbms_resource_manager.calibrate_io and provided as input 18 disks and max latency of 10. The values in dba_ rsrc_io_calibrate are latency 12, num_physical_disks 18. 12 is greater than the max value I provided, I know that the number of disks is just what I gave it when I executed.
Ok, I ran it again, changing the max_latency to 20 - more than the 12 returned from the previous run.
Latency returned was 15. So now I want to see what happens when I really set the max allowable latency up, go to the max 100. Latency reported in the table is now 61.
I've read the Oracle doc, maybe I missed something. I've looked at Doug Burns's write up http://oracledoug.com/serendipity/index.php?/archives/1319-Parallel-Query-and-11g.html
Jeff Moss's work
http://www.oramoss.com/blog/2007/09/11g-io-calibration-tool.html
And asked Mike Ault for insite, he of course got very good number, and ran the procedure using the number of phsical disks, and since he is mirroring, 1/2 the number of phycial disks, and got the same out put both times.
But I've not been able to find out an answer about how to determine the correct setting for physical disks, as noted above, or what setting latency really does.
Does setting latency to it's max value, really get you the best idea of the capabilities of your disk subsystem, or should you set it at what you think the disk subsystem should be able to perform?