RE: Disk Device Busy (%) - What exactly is this?
Date: Mon, 21 Nov 2011 09:55:34 -0600
Message-ID: <C5533BD628A9524496D63801704AE56D6A33D07D46_at_SPOBMEXC14.adprod.directory>
I'm not sure how any OS "knows" the maximum IO bandwidth available to a specific device (especially LUNs) but "Device Busy (%)" is common metric available on both *nix and Windows systems.
On many Linux systems, you can run iostat -x 2 100 and get interval snapshots showing the disk busy percentage (or disk utilization percentage). In Windows you use perfmon and the Logical (or Physical) disk metric counters.
Theoretically the percentage should never be higher than 100%. Also you should notice disk queues increasing and average waits the closer you get to 100% busy.
Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205
"Quality is never an accident; it is always the result of intelligent effort."
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-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Guillermo Alan Bort
Sent: Monday, November 21, 2011 9:45 AM
To: oracle-l-freelists
Subject: Disk Device Busy (%) - What exactly is this?
hi guys,
recently we got an alert from OEM on the metric Disk Device Busy (%) (it was at about 99% or something like that).
My Oracle Forums and Metalink search yielded some interesting results that say it's a false alert (what a shock!)
So, the Documentation points to space utilization: http://download-east.oracle.com/docs/cd/B16240_01/doc/em.102/b16230/host.htm#BHAFEBDG
Metalink corrects this as a documentation bug (another shock!)
The description of the metric in the documentation leads us to believe that the metric checks the disk capacity. But this is incorrect and we have a documentation bug
Bug.5099684 : EXPLANATION OF DISK DEVICE BUSY METRIC IS WRONG:
In reality, this metric checks how 'busy" the disk is.
So... what on earth does "busy" mean? Is it some sort of metric of how much I/O is being done on the disk? if so... how can this be a percentage? What's 100%?
I don't much care for the alert as I'm pretty sure that it's either a false alert or something I can't do anything about in the short run... but I would like to know what I'm seeing so I can find a way to prevent it from happening again.
Oh, the databases are on SAN with one of those cool raid 5 stripped across 50 disks or something. So I get LUNs, not physical disks. Does this mean a particular LUN is busy?
Thanks
Alan.-
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Received on Mon Nov 21 2011 - 09:55:34 CST