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

From: Guillermo Alan Bort <cicciuxdba_at_gmail.com>
Date: Mon, 21 Nov 2011 13:15:20 -0300
Message-ID: <CAJ2dSGRudybXcg8z_1B2o6mFyCs2FegTg-vqHvDRrBRJPMmOmA_at_mail.gmail.com>

Dimitre,
  From that document I gather that the iostat busy metric is not all that reliable when you have a complex disk subsystem: from the document: *"Wrap up*
So the real answer to our initial question is that the model of disk behavior and performance that is embodied by the iostat report is too simple to cope with the reality of a complex underlying disk subsystem. We stay with the old report to be consistent and to offer users familiar data, but in reality, a much more sophisticated approach is required. I'm working (slowly) on figuring out how to monitor and report on complex devices like this."

It did, however, shed some light on exactly what "disk device busy (%)" means.

thanks for the replies.
Alan.-

On Mon, Nov 21, 2011 at 12:56 PM, Radoulov, Dimitre <cichomitiko_at_gmail.com>wrote:

>
> Hi,
> I have always considered the iostat/sar -d busy metrics important.
> When I saw your question I searched google again and I found this *old*
> document
> that seems useful:
>
> sunsite.uakom.sk/**sunworldonline/swol-08-1999/**swol-08-perf.html<http://sunsite.uakom.sk/sunworldonline/swol-08-1999/swol-08-perf.html>
>
>
> Hope this helps
> Dimitre
>
>
> On 21/11/2011 16:45, Guillermo Alan Bort wrote:
>
>> 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<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<http://www.freelists.org/webpage/oracle-l>
>>
>>
>>
>

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Received on Mon Nov 21 2011 - 10:15:20 CST