OpenVMS Bad Block Locator Utility Manual

This document serves as a manual for the OpenVMS Bad Block Locator Utility (BAD), designed for VMS system managers, operators, and system programmers. Its primary function is to identify and record unreliable data storage blocks, known as bad blocks, on block-addressable devices.

The utility operates by writing test patterns to each block on a medium, reading the data back, and comparing it to the original pattern. If the data does not match, the block is deemed unreliable. Bad block addresses are recorded in the Software Detected Bad Block File (SDBBF), which is part of the larger Detected Bad Block File (DBBF).

To use BAD, users must first allocate the device with the ALLOCATE command and then mount it as FOREIGN using MOUNT/FOREIGN. The utility is invoked via the ANALYZE/MEDIA DCL command. It is crucial to note that running BAD with the /EXERCISE qualifier destroys all existing data on the device, as it purges the volume during testing. However, the DBBF can be updated without data destruction using /NOEXERCISE and /BAD_BLOCKS. After bad blocks are located, the INITIALIZE command can reformat the volume to Files-11 format and allocate these blocks to a special file ([000000]BADBLK.SYS), preventing their use.

The DBBF's location and entry format vary based on whether the device is a "last-track" or "non-last-track" device. Last-track devices store DBBF information on their last track, while non-last-track devices create it on the last good block. The DBBF has a maximum capacity of 126 entries.

The manual also details various qualifiers for the ANALYZE/MEDIA command, including /BAD_BLOCKS (to add bad block locations), /EXERCISE (to control media testing and data preservation), /LOG (to report bad block counts), /OUTPUT (to direct DBBF contents to a file), /RETRY (to enable soft error retries), and /SHOW (to list DBBF contents). It emphasizes that BAD is not necessary for Mass Storage Control Protocol (MSCP) devices, as they automatically re-vector bad blocks. This manual applies to OpenVMS AXP Version 1.5 and OpenVMS VAX Version 6.0.