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Re: disk.dev.avactive and disk.dev.aveq on RH Advanced Server

To: "Davis, Todd C" <todd.c.davis@xxxxxxxxx>
Subject: Re: disk.dev.avactive and disk.dev.aveq on RH Advanced Server
From: kenmcd@xxxxxxxxxxxxxxxxx
Date: Sun, 13 Apr 2003 09:11:05 +1000 (EST)
Cc: "'pcp@xxxxxxxxxxx'" <pcp@xxxxxxxxxxx>
In-reply-to: <29AD895CE780D511A8870002A50A666D04F90983@xxxxxxxxxxxxxxxxxxxxxx>
Reply-to: kenmcd@xxxxxxxxxxxxxxxxx
Sender: pcp-bounce@xxxxxxxxxxx
Apart from the scaling problem in the Linux PMDA that Todd reported later
with disk.dev.avactive and disk.dev.aveq, I am unaware of any problems
with these metrics.

Since the time metrics are in units of msec, these numbers ...

> Average_disk_utilization (Tue Mar 18 11:09:09 2003):
>     localhost: [sda] 10.0
> Average_queue_length (Tue Mar 18 11:09:09 2003):
>     localhost: [sda] 30.1

are time utilizations, so it looks like the numbers here are before the
fix to remove the incorrect * 1000 / HZ scaling in the PMDA (the active
number reported here should be in the range 0.0 to 1.0).

It looks to me as though your sard patch may well have some sort
of race condition where it "loses" the completion processing for
one or more (I'd guess 3 given the aveq value) I/Os.

We have seen no evidence on our local 2.4.17, 2.4.18 and 2.4.20
kernels ... but we are not running RH AS.

On Tue, 18 Mar 2003, Davis, Todd C wrote:

> 
> With no disk activity on the system I see disk.dev.avactive and
> disk.dev.aveq on the root drive. The last sample had some disk io but the
> disk.dev.avactive number did not change and disk.dev.aveq number did not
> change significantly. Are these metrics supposed to me accurate? They look
> bogus to me. 
> 
> I am running RetHat Advanced Sever with a 2.4.18 kernel with the sard patch
> applied.
> 
> The script:
> 
> pmie -f -e -V <<pmie.end
> //
> // Watch average disk utilization and average queue length
> //
> myhost = "localhost";                 // the host of interest
> delta = 3 sec;
> Block_total =
>     disk.dev.blktotal :\$myhost;
> Average_disk_utilization =
>     disk.dev.avactive :\$myhost;
> Average_queue_length =
>     disk.dev.aveq :\$myhost;
> 
> pmie.end
> 
> The output:
> 
> Block_total (Tue Mar 18 11:09:06 2003): ? ?
> Average_disk_utilization (Tue Mar 18 11:09:06 2003): ? ?
> Average_queue_length (Tue Mar 18 11:09:06 2003): ? ?
> 
> Block_total (Tue Mar 18 11:09:09 2003):
>     localhost: [sda] 0
>     localhost: [sdb] 0
> Average_disk_utilization (Tue Mar 18 11:09:09 2003):
>     localhost: [sda] 10.0
>     localhost: [sdb] 0
> Average_queue_length (Tue Mar 18 11:09:09 2003):
>     localhost: [sda] 30.1
>     localhost: [sdb] 0
> 
> Block_total (Tue Mar 18 11:09:12 2003):
>     localhost: [sda] 0
>     localhost: [sdb] 0
> Average_disk_utilization (Tue Mar 18 11:09:12 2003):
>     localhost: [sda] 10.0
>     localhost: [sdb] 0
> Average_queue_length (Tue Mar 18 11:09:12 2003):
>     localhost: [sda] 30.0
>     localhost: [sdb] 0
> 
> Block_total (Tue Mar 18 11:09:15 2003):
>     localhost: [sda] 0
>     localhost: [sdb] 0
> Average_disk_utilization (Tue Mar 18 11:09:15 2003):
>     localhost: [sda] 10.0
>     localhost: [sdb] 0
> Average_queue_length (Tue Mar 18 11:09:15 2003):
>     localhost: [sda] 30.0
>     localhost: [sdb] 0
> 
> Block_total (Tue Mar 18 11:09:18 2003):
>     localhost: [sda] 0
>     localhost: [sdb] 0
> Average_disk_utilization (Tue Mar 18 11:09:18 2003):
>     localhost: [sda] 10.0
>     localhost: [sdb] 0
> Average_queue_length (Tue Mar 18 11:09:18 2003):
>     localhost: [sda] 30.0
>     localhost: [sdb] 0
> 
> Block_total (Tue Mar 18 11:09:21 2003):
>     localhost: [sda] 85
>     localhost: [sdb] 0
> Average_disk_utilization (Tue Mar 18 11:09:21 2003):
>     localhost: [sda] 10.0
>     localhost: [sdb] 0
> Average_queue_length (Tue Mar 18 11:09:21 2003):
>     localhost: [sda] 30.9
>     localhost: [sdb] 0
> 
> Todd C. Davis
> These are my opinions and absolutely not official opinions of Intel Corp.
> Telco Systems Development
> Intel Corporation, Columbia Design Center
> CBA-2, Suite 100
> 250 Berry Hill Road
> Columbia, SC 29210
> (803) 461-6108
> fax:: (803) 461-6292
> mailto:todd.c.davis@xxxxxxxxx
>  
> 
> 





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