How can I get performance data on tape devices using iostat in Red Hat Enterprise Linux 4?

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Release found: Red Hat® Enterprise Linux® 4 Update 2 or later

Resolution:
When examining block-device performance, the iostat command is a highly useful tool, providing data on the number of block reads and writes per second. This enables throughput to be calculated for a device. This same capability is not present for character devices such as tape drives. Instead, similar functionality can be achieved using Systemtap, provided in Red Hat Enterprise Linux 4 Update 2 and later.

The following instructions allow iostat -like functionality for the tape drives, and can readily be extended to other character devices. Follow the procedure given below:

1. Ensure that systemtap is installed:

   # rpm -qa | grep systemtap
   

   If the package is not installed, install the systemtap package by the following command:

   # up2date systemtap
   

2. Install the kernel-debuginfo package. In order for systemtap to work, the kernel-debuginfo package for the current kernel should be installed. These are not available via Red Hat Network (RHN), but can be downloaded from ftp://ftp.redhat.com/pub/redhat/linux/updates/enterprise/

   for the particular version of Red Hat Enterprise Linux. It should be of the exact same version as the kernel, for example: If the kernel version is kernel-2.6.9-34.0.1.EL.i686, download kernel-debuginfo-2.6.9-34.0.1.EL.i686.rpm and install it:

   # rpm -ivh kernel-debuginfo-`uname -r`.i386.rpm
   

3. Obtain the iostat-scsi Red Hat Enterprise Linux 4 Systemtap script

   The iostat-scsi script was written by Frank Ch. Eigler. This can be obtained from http://sourceware.org/systemtap/wiki/WSiostatSCSI.
   Download the iostat-scsi-rhel4.stp file, which is a version of iostat-scsi that
   will work with Red Hat Enterprise Linux 4.

4. Run the script using Systemtap

   Run the script using the stap command. The script
   takes a parameter, like iostat, which is the interval
   between output. In this instance, the parameter is in milliseconds, not
   seconds. This is due to the Red Hat Enterprise Linux 4 version of systemtap.

   # stap iostat-scsi.stp 1000
     Device:       tps blk_read/s blk_wrtn/s  blk_read  blk_wrtn
         sda      3.00      0.00     64.00         0        64
         st1     42.00      0.00 172032.00         0    172032
   
         sda      0.00      0.00      0.00         0         0
         st1     40.00      0.00 163840.00         0    163840
   
         sda      0.00      0.00      0.00         0         0
         st1     45.00      0.00 184320.00         0    184320
   

   The throughput information is presented in the same format as iostat. Block size is set by the script to be 512 bytes.

contributed by Andrew Ryan

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