RE: Disk Device Busy (%) - What exactly is this?

There are real IO limits on the following: 1.) LUNS themselves (how many disks in the stripe, RAID levels) 2.) IO Controller Card between the server and the LUN or disk

NOW, the question that 'should be' asked is:

"How does my OS determine the IO capacity of my storage?"

Imagine if the OS does a statistics gathering on the IO subsystem (much like Oracle does on tables) then it can possibly "know" within a reasonable margin of error what the expected IO bandwidth is for the storage system (regardless of whether or not it is a LUN or a DISK).

So, does ANYONE know how the OS (Windows, Linux etc) tries to determine the maximum IO available across a disk or LUN?

Chris Taylor
Sr. Oracle DBA
Ingram Barge Company
Nashville, TN 37205

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-- John Ruskin (English Writer 1819-1900)

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-----Original Message-----
From: oracle-l-bounce_at_freelists.org [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Radoulov, Dimitre Sent: Monday, November 21, 2011 10:21 AM To: Guillermo Alan Bort
Cc: oracle-l-freelists
Subject: Re: Disk Device Busy (%) - What exactly is this?

Hi Alan,
yes, this was new to me too. In another mail Grzegorz Goryszewski have just posted a link to an article by Alex Gorbachev, which seem to confirm that too:

Quoting it:

Traditionally, it's common to assume that the closer to 100% utilization a device is, the more saturated it is. This might be true when the system device corresponds to a single physical disk. However, with devices representing a LUN of a modern storage box, the story might be completely different. [...]

Regards
Dimitre

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