ADDBAD(8)

NAME
addbad - modify dec standard 144 bad sector information

SYNOPSIS
/etc/addbad disktype disk -m [ bad ... ]

DESCRIPTION
Addbad is used to identify bad sectors on a disk containing otherwise good file systems. It can also be used to inspect the information stored on a disk that is used by the disk drivers to implement bad sector forwarding. The format of the information is specified by DEC standard 144 (as extended by Sequent), as follows.

The bad sector data is located in the last track of the disk. There are five identical copies of each block of the data. The first block, relative block 0, is located in the first 5 even-numbered sectors of the track. The second block (if any) is located in the first five odd-numbered sectors of the track. The third block (if any) is located in sectors 10-14 of the track. Subsequent blocks (if any) are located in subsequent five-block contiguous groups.

Replacement sectors are allocated starting with the first sector before the bad sector information and working backwards towards the beginning of the disk. The position of the bad sector in the bad sector table determines which replacement sector it corresponds to. The bad sectors must be listed in ascending order.

The bad sector information and replacement sectors are conventionally only accessible through the ``c'' file system partition of the disk. If that partition is used for a file system, the user is responsible for making sure that it does not overlap the bad sector information or any replacement sectors.

The bad sector structure is described in /usr/sys/mbad/dkbad.h.

Addbad is invoked by giving a device type (e.g. eagle), and a device name (e.g. xp0, xp1, etc.). If there are no other arguments, it reads the first sector of the last track of the corresponding disk and prints out the bad sector information. Otherwise, it takes a list of bad sectors, and will mark the sectors bad and add them to the list on disk. The bad sectors are identified in error messages that are generated by DYNIX. These error messages are described in xp(4). Addbad rearranges the replacement sectors as needed, and attempts to copy each of the listed sectors to a replacement sector. The contents of all files on the disk are preserved.

NOTE: this can only be done safely when there is no other disk activity, preferably while running single-user.

Sectors can only be marked bad by root. It is necessary to reboot before the change will take effect.

This program should be used with care, since sectors marked bad cannot be made good again without reformatting the disk. The initial bad sector list should be generated using the disk formatter, or if that is not possible, with bad144.

The -m flag instructs addbad to display the manufacturer's bad-block sectors in cylinder/track/byte-offset format. This information is needed to reformat the disk.

SEE ALSO
xp(4), zd(4), bad144(8), badsect(8), xpformat(8S), zdformat(8S)

BUGS
It should be possible to format disks on-line under UNIX.

Sector numbers are physical sectors, not logical block numbers (as usually reported by DYNIX).