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

From: Guillermo Alan Bort <cicciuxdba_at_gmail.com>
Date: Mon, 21 Nov 2011 12:45:18 -0300
Message-ID: <CAJ2dSGRhRnEMqvQ06VJapdgKu0JpgorW7noyWuARFaGxhYNcfw_at_mail.gmail.com>

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.-

--
http://www.freelists.org/webpage/oracle-l

Received on Mon Nov 21 2011 - 09:45:18 CST