Summary sar -u output

From: Geert Touquet (Geert.Touquet@uz.kuleuven.ac.be)
Date: Mon Feb 13 1995 - 05:52:09 CST


Hello

Original question:
> >I have a question about saroutput. We have a Sparsserver 2000 with 6 cpu.
> >On the machine there is one process that do a lot of I/O on one disk.
> >The other processes don't need this disk and do not a lot of I/O. The sar
> >output give us that %idle is about +/- 8 % and waiting for I/O completion
> >is 70%.
> >
> >vmstat 5 give us a idle time about 60 %.
> >Normally, I expect that sar output should be about idle time +/- 50 %
> >and %wio +/- 10 % (for the one process that do a lot of I/O)
> >
> >Give program 'sar' us a wrong output or I do a wrong interpretation ??
 
 1. The sar -u output is in sync with vmstat 5 output You may
    want to run "sar -u 5 100," "vmstat 5," and "iostat -tx 5" at the
    same time.
 
 2. The id column in vmstat 5 output is the sum of %wio and %idle in
    sar -u
 
 3. Because of only one process doing a lot of I/O and your SPARCcenter
   2000 with, I imagine, more than one processor, "mpstat 5" may be a
    better tool than vmstat 5.
 

The definition of % waiting for I/O completion means that 70% of the time,
there is at least one process waiting for I/O, and *no other runnable
processes* in the same time interval.

There is one thing that is rare. There is one process that use
a lot of I/O but all processors have % waiting about 70 %. Is that
normal ?

Thanks Birger A. Wathne and Anchi Zhang

        Touquet Geert

-- 
-- 
Geert Touquet            E-mail : Geert.Touquet@uz.kuleuven.ac.be     
                         Mail :   Universitaire Ziekenhuizen Leuven
                                  Kapucijnenvoer 33
Phone  : +(32) 16 33 29 77        B-3000 Leuven, Belgium
 



This archive was generated by hypermail 2.1.2 : Fri Sep 28 2001 - 23:10:16 CDT