HP OpenVMS System Manager's Manual, Volume 1:...

Managing Storage Media

Using Interrupt Priority Level C (IPC)

Using Files and Directories

Using the Bad Block Locator Utility to Detect Media Errors  

Many newer devices automatically check for bad blocks; therefore, BAD is more useful with older devices that do not check for bad blocks.

• Writes a test pattern to each block on the media



• Reads the contents of the block into a buffer



• Compares the data read back with the data written

If the data does not compare exactly, a block cannot reliably store data.

When the Bad Block Locator utility locates a bad block, it records the address of the block. Consecutive bad blocks are recorded as single entries for non-last-track devices. After it finishes testing the disk, BAD writes the addresses of the bad blocks into a file called the detected bad block file (DBBF).

Testing a volume for bad blocks destroys its contents. However, you can update the detected bad block file (DBBF) without erasing the contents of the volume by using the ANALYZE/MEDIA qualifiers /NOEXERCISE and /BAD_BLOCKS.

To use BAD, perform the following steps:

1. Allocate the device with the DCL command ALLOCATE (to ensure that the device is not accessed by any other programs).
2. Enter the DCL command MOUNT/FOREIGN.
   
   When the device is mounted as foreign, the system does not recognize it as a Files-11 volume, and BAD can execute.
3. Enter the DCL command ANALYZE/MEDIA.

Refer to online help or to the archived manual OpenVMS Bad Block Locator Utility Manual for details on using the Bad Block Locator utility.

Using Interrupt Priority Level C (IPC)

Using Files and Directories