strange Waiting for IO numbers

strange Waiting for IO numbers

Post by J » Sun, 02 Mar 2003 09:24:09



Greetings.

I have a bit of an issue.

I have a Sun 220R running Oracle and Solaris 2.6.

I notice that my sar report today shows 0% idle time and near 100%
waiting for IO time.

I cant see any degredation in performance at all.  iostat doesnt show
anything wrong, in fact it shows the disks and nearly all idle.  The
%b on the disks are almost always zero, its a lightly used dev. box.

So how can I find out what is causing this?  Top shows high wio.  The
weird thing is that vmstat shows 100% idle time.

All swap is free and there is nothing in the sr column of vmstat , so
I am assuming its not anything to do with memory.

I dont see any errors in the messages file.

So some process must be waiting for IO, but how can I tell?

Tks

 
 
 

strange Waiting for IO numbers

Post by Darren Dunha » Sun, 02 Mar 2003 10:12:06



> Greetings.
> I have a bit of an issue.
> I have a Sun 220R running Oracle and Solaris 2.6.
> I notice that my sar report today shows 0% idle time and near 100%
> waiting for IO time.

Noted that I/O time is just a subset if idle time.

Quote:> I cant see any degredation in performance at all.

Okay.

Quote:> iostat doesnt show
> anything wrong, in fact it shows the disks and nearly all idle.  The
> %b on the disks are almost always zero, its a lightly used dev. box.

Right.

Quote:> So how can I find out what is causing this?  Top shows high wio.  The
> weird thing is that vmstat shows 100% idle time.

Right.  Vmstat doesn't break out the idle time into idle(io) and
idle(non-io) like iostat does.

All idle(io) means is that the cpu has nothing to do at the moment, and
at least one program is sleeping while waiting for I/O to complete.

This could be a 'mt' program trying to talk to a borked tape drive.  It
could be most anything.

In 'vmstat', is your 'b' column at least 1?  That's representing the
blocked process.

Now as to which process that is, it's more difficult to tell.

Look at your system and see if there's a process that shouldn't be
there.  Anything associated with tapes or other I/O devices?

Quote:> So some process must be waiting for IO, but how can I tell?

Yup.  It's hard.  Presumably you could write a program to go look around
in the proc structures.  I couldn't tell you how to do that though..

--

Unix System Administrator                    Taos - The SysAdmin Company
Got some Dr Pepper?                           San Francisco, CA bay area
         < This line left intentionally blank to confuse you. >

 
 
 

strange Waiting for IO numbers

Post by J » Wed, 05 Mar 2003 05:59:25




> > Greetings.

> > I have a bit of an issue.

> > I have a Sun 220R running Oracle and Solaris 2.6.

> > I notice that my sar report today shows 0% idle time and near 100%
> > waiting for IO time.

> Noted that I/O time is just a subset if idle time.

> > I cant see any degredation in performance at all.

> Okay.

> > iostat doesnt show
> > anything wrong, in fact it shows the disks and nearly all idle.  The
> > %b on the disks are almost always zero, its a lightly used dev. box.

> Right.

> > So how can I find out what is causing this?  Top shows high wio.  The
> > weird thing is that vmstat shows 100% idle time.

> Right.  Vmstat doesn't break out the idle time into idle(io) and
> idle(non-io) like iostat does.

> All idle(io) means is that the cpu has nothing to do at the moment, and
> at least one program is sleeping while waiting for I/O to complete.

> This could be a 'mt' program trying to talk to a borked tape drive.  It
> could be most anything.

> In 'vmstat', is your 'b' column at least 1?  That's representing the
> blocked process.

> Now as to which process that is, it's more difficult to tell.

> Look at your system and see if there's a process that shouldn't be
> there.  Anything associated with tapes or other I/O devices?

> > So some process must be waiting for IO, but how can I tell?

> Yup.  It's hard.  Presumably you could write a program to go look around
> in the proc structures.  I couldn't tell you how to do that though..

Darren, I hope to be as talented as you one day!

It was an mt process from a job on another box, the tape drive was not
functioning properly, poped the tape out and inserted a new one, no
problem.

Thanks!

-jc