BAD144(8)

NAME
bad144 - read/write dec standard 144 bad sector information

SYNOPSIS
/etc/bad144 [ -f ] disktype disk [ sno [ bad ... ] ]

DESCRIPTION
Bad144 can 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.

Bad144 is invoked by giving a device type (e.g. eagle), and a device name (e.g. xp0, xp1, etc.). It reads the first sector of the last track of the corresponding disk and prints out the bad sector information. It may also be invoked giving a serial number for the pack and a list of bad sectors, and will then write the supplied information onto the same location. Note, however, that bad144 does not arrange for the specified sectors to be marked bad in this case. This option should only be used to restore known bad sector information which was destroyed. It is necessary to reboot before the change will take effect.

If the disk is a Fujitsu Eagle, the -f option may be used to mark the bad sectors as ``bad''. NOTE: this can only be done safely when there is no other disk activity, preferably while running single-user. Otherwise, new bad sectors can be added only by running a formatter. Note that the order in which the sectors are listed determines which sectors used for replacements; if new sectors are being inserted into the list on a drive that is in use, care should be taken that replacements for existing bad sectors have the correct contents.

SEE ALSO
addbad(8), badsect(8).

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

It should be possible to mark bad sectors on drives of all types.

The drivers which write a system core image on disk after a crash do not handle errors; thus the crash dump area must be free of errors and bad sectors.