ioscan disk load

[Jeong Jin-wook]

My customer complain about io performance.
In application sorece code, they run ioscan -fn per 2sec. I looked at glance disk io 100% when ioscan is run. My customer want me to explain how ioscan work. Why it cause disk load. Any one explain for me?

[Peter Godron]

Hi,
man ioscan
"ioscan scans system hardware, usable I/O system devices, or kernel I/O system data structures as appropriate, and lists the results. For each hardware module on the system, ioscan displays by default the hardware path to the hardware module, the class of the hardware module, and a brief description."

Ioscan has to scan the actual hardware unless the -k parameter is used, so will cause disk load. Why is the application scanning every 2 seconds ?

[Hein van den Heuvel]

ioscan goes out and pokes the disk.

The name does imply that, does it not?

It wouldn't surprise me if it even did an operation like "everybody quiet now, let me hear from any new kids on the block". And "John where are you? I know you are out there John I saw you earlier, stop hiding John, oh well John does not want to play anymore".

I must assume this is a system monitor application of some sort?

running ioscan once per 2 second seems too intense! Want to reduce the load by a factor of thousand? run it once every 2000 seconds, or on demand.

How often is the configuration expected to change?!

If it is probing to 'see' whether a particular set of disks is still accesible, in order to be able to give early failure warnings then do just that: write a script (or better still a program) to read (and/or write?) data from(to) a list of mountpoints or devices. Don't use the ioscan sledgehammer!

fwiw,
Hein.

[spex]

Jeong,

'ioscan' is the wrong utility for this application. Look into using the system activity report package ('man 1m sa1'), Event Monitoring Service ('man 5 ems'), or something in the OpenView product line-up, such as GlancePlus (http://h20229.www2.hp.com/products/gppak2k/index.html).

PCS

[James R. Ferguson]

Hi:

As noted, 'ioscan' is an intensive (resource-wise) probe of your hardware and running it frequently will certainly affect your performance!

That said, however, you can reduce the work it does if you only need to find what the kernel tables currently know. Simply add the '-k' option:

# ioscan -kfn

Regards!

...JRF...

[Bill Hassell]

ioscan is a VERY disruptive tool and should NEVER be run every few seconds (or minutes for that matter). ioscan by default runs very low-level probes on every I/O card, and on disk connections, runs scans to determine what disks might be attached. It will be VERY slow (many seconds to minutes) if you have hundreds of disk devices such as an array.

Now ioscan -k will return immediately since the details are simply reported from memory -- no scan takes place. But even with the low overhead using -k, ioscan should NEVER be used to monitor a system. It is not a performance tool, it is an inventory tool and might be run once in the evening as part of a hardware inventory script. You need to question the reason ioscan is being run every 2 seconds.