11-13-2007
First off: if you tar something, the command will read something on your disk (a bunch of files) and then create an archive from it, writing that to the disk (most of times). What else then seeing activity on your disk do you suppose will happen?
Additionally i would like to clarify what the "% tm_act" field in the output of iostat means:
The OS has a sensor, regularily asking the disk if it is busy or not. When the disks aswers half of the times "I'm busy", then the "% tm_act" will be 50%. If the disk answers every time "I'm busy" then tm_act will be 100%, etc.. A disk answers with "busy", when there are requested operations not yet fulfilled, read or write. If many very small requests go to the disk the chance of the sensor asking exactly when one such operation is still open goes up - much more so than the real activity of the disk.
So, "100% busy" does not necessarily mean the disk is at the edge of its trasnfer bandwidth. It could mean either that because the disk is getting relatively few but big requests (example: stream I/O) but it could also mean that the disk is getting a lot of requests which are relatively small so that the disk is occupied most of the time, but not using its complete transfer bandwith.
To find out which is the case analyse the corresponding "Kb_read" and "Kb_wrtn" column from iostat. You know how much a modern disk drive can approximately handle (~17MB/second) physically and bypassing any cache. Compare your data to this (rule-of-thumb-)value and you will get a more detailed picture.
bakunin
Last edited by bakunin; 11-13-2007 at 08:42 AM..
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LEARN ABOUT REDHAT
longrun
LONGRUN(1) General Commands Manual LONGRUN(1)
NAME
Transmeta(TM) Crusoe(TM) LongRun(TM) utility
SYNOPSIS
longrun [-c device] [-m device] [-hlpv] [-f flag] [-s low high]
DESCRIPTION
The longrun utility is used to control and query LongRun settings on Transmeta Crusoe processors.
-c device
Set the CPUID device. The default CPUID device is /dev/cpu/0/cpuid.
-m device
Set the MSR device. The default CPUID device is /dev/cpu/0/msr.
-h Print help.
-l List LongRun information about available performance levels for the CPU.
The following values are reported on all Transmeta CPUs that implement LongRun.
% An available performance level, expressed as a percentage of range of available core CPU frequencies. 0 corresponds to
the lowest available frequency and 100 corresponds to the highest.
MHz The core CPU frequency at that level.
Volts The core CPU voltage at that level.
usage The power usage relative to the maximum performance level.
-p Print current LongRun settings and status: whether LongRun is enabled, whether LongRun Thermal Extensions are active, the current
LongRun performance window (expressed as a percentile range), the current LongRun performance level (expressed as a percentile), and
the current LongRun flags.
-v Be more verbose.
-f flag
Set a LongRun mode flag. Currently, the two supported flags are performance and economy. This controls whether the processor is in
"performance mode" or "economy mode".
-s low high
Set the current LongRun performance window as a percentile range. The low number cannot be greater than the high number. The
minimum and maximum performance values accepted by the CPU are 0 and 100, respectively.
ENVIRONMENT
No environment variables are used.
FILES
This program requires that the Linux CPUID and MSR devices be compiled into the kernel (or loaded as kernel modules), that the CPUID
character device be readable, and that the MSR character device be both readable and writable.
SEE ALSO
acpid(8), apmd(8), hdparm(8)
AUTHOR
Daniel Quinlan <quinlan@transmeta.com>
February 14, 2001 LONGRUN(1)