Measuring disk performance with the SKIP_DISK_WRITES touch file

Article:HOWTO56132  |  Created: 2011-07-25  |  Updated: 2013-08-22  |  Article URL
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Measuring disk performance with the SKIP_DISK_WRITES touch file

The SKIP_DISK_WRITES procedure can be used on UNIX or Windows.

The SKIP_DISK_WRITES procedure is a useful follow-on to the bpbkar procedure. The bpbkar procedure may show that the disk read performance is not the bottleneck. If it is not the bottleneck, the bottleneck is in the data transfer between the client bpbkar process and the server bpdm process. The following SKIP_DISK_WRITES procedure may be helpful.

If the SKIP_DISK_WRITES procedure shows poor performance, the problem may involve the network, or shared memory (such as not enough buffers, or buffers that are too small). You can change shared memory settings.

You can change shared memory settings.

See About shared memory (number and size of data buffers)


The following procedure can lead to data loss. The SKIP_DISK_WRITES touch file disables all backup data write operations for disk. It not recommended to touch this file on a production server or data lost will occur. Disable active production policies for the duration of this test. You must remove the touch file when this test is complete. (See step 7 below.)

To measure disk I/O using the SKIP_DISK_WRITES touch file

  1. Create a new disk storage unit, with /tmp or some other directory as the image directory path.

  2. Create a policy that uses the new disk storage unit.

  3. Deactivate any active production policies for the duration of this test.

  4. Enter the following:





    This file disables all data-write operations for disk backups but retains the creation of disk fragments and associated metadata.

  5. Run a backup from this policy.

    NetBackup creates a file in the storage unit directory as if this backup is a real backup to disk. The image file is 0 bytes long.

  6. To remove the zero-length file and clear the NetBackup catalog of a backup that cannot be restored, run this command:


    /usr/openv/netbackup/bin/admincmd/bpexpdate -backupid backupid -d 0


    install_path\Netbackup\bin\admincmd\bpexpdate -backupid backupid -d 0

    where backupid is the name of the file that resides in the storage unit directory.

  7. Remove the SKIP_DISK_WRITES file.

  8. Re-activate any policies that were deactivated for this procedure.

See Measuring disk performance with bpbkar.

See About measuring performance independent of tape or disk output.


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