Isilon: How to create test files using the dd command

Introduction

How to quickly create test files of a specific size using the UNIX "direct disk" utility, the "dd" command. For more information about the dd Command and its options, run the following command from the command line to view its manual:

man dd

Procedure

1. Open an SSH connection on any node in the cluster and log in using the "root" account.
2. Create a 100MB zero-padded file by running the following command. This is useful to create large files whose contents are not important.
    

   dd if=/dev/zero of=zero-padded.bin bs=1024 count=102400

    
3. Create a 100MB file of random data by running the following command. This is useful for creating multiple files whose data differs (for example, when testing utilities that examine the differences in files):
    

   dd if=/dev/urandom of=random-data.bin bs=104857600 count=1

    
4. Create a 100MB sparse file that takes up no space on disk by running the following command. This is useful for resizing binary image files without overwriting them.
    

   dd if=/dev/zero of=sparse-file.bin bs=1 count=0 seek=104857600

   
   Then verify the real and apparent size of the sparse file.
    
   1. Verify the real size of the sparse file by running the following command:
       

      du -A sparse-file.bin

      
      Output similar to the following is displayed, indicating that the file uses 0MB of space on the disk:
       

      0 sparse-file.bin

       
   2. Verify the apparent size of the sparse file by running the following command:
       

      ls -lh sparse-file.bin

      
      Output similar to the following is displayed, indicating that the file appears to consume 100MB of space on the disk:

      -rw-------     1 root  wheel   100M Jul  1 20:35 sparse-file.bin
      

Requisite tools or skills

The procedures in this article require a familiarity with the OneFS operating system and UNIX commands and be comfortable running commands from the command-line interface.