BAD144(8)

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

SYNOPSIS
bad144 [-c] [-f] [-v] disk [ sno [bad ...]]
bad144 -a [-c] [-f] [-v] disk [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 bad144 tool is only installed on supported platforms.

Available options:

-a  The argument list consists of new bad sectors to be added to an existing list. The new sectors are sorted into the list, which must have been in order. Replacement sectors are moved to accommodate the additions; the new replacement sectors are cleared.

-c  Forces an attempt to copy the old sector to the replacement, and may be useful when replacing an unreliable sector.

-f  (vax only) For a RP06, RM03, RM05, Fujitsu Eagle, or SMD disk on a MASSBUS, the -f option may be used to mark the new bad sectors as ``bad'' by reformatting them as unusable sectors. This option is required unless the sectors have already been marked bad, or the system will not be notified that it should use the replacement sector. This option may be used while running multiuser; it is no longer necessary to perform format operations while running single-user.

-v  The entire process is described as it happens in gory detail if -v (verbose) is given.

The format of the information is specified by DEC standard 144, as follows. The bad sector information is located in the first 5 even numbered sectors of the last track of the disk pack. There are five identical copies of the information, described by the dkbad structure.

Replacement sectors are allocated starting with the first sector before the bad sector information and working backwards towards the beginning of the disk. A maximum of 126 bad sectors are supported. The position of the bad sector in the bad sector table determines the replacement sector to which it corresponds. 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. Thus, one track plus 126 sectors must be reserved to allow use of all of the possible bad sector replacements.

The bad sector structure is as follows:

    struct dkbad {
    	int32_t   bt_csn;		/* cartridge serial number */
    	u_int16_t bt_mbz;		/* unused; should be 0 */
    	u_int16_t bt_flag;		/* -1 = alignment cartridge */
    	struct bt_bad {
    		u_int16_t bt_cyl;	/* cylinder number of bad sector */
    		u_int16_t bt_trksec;	/* track and sector number */
    	} bt_bad[126];
    };

Unused slots in the bt_bad array are filled with all bits set, a putatively illegal value.

bad144 is invoked by giving a device name (e.g. wd0, hk0, hp1, etc.). With no optional arguments it reads the first sector of the last track of the corresponding disk and prints out the bad sector information. It issues a warning if the bad sectors are out of order. bad144 may also be invoked with a serial number for the pack and a list of bad sectors. It will write the supplied information into all copies of the bad-sector file, replacing any previous information. Note, however, that bad144 does not arrange for the specified sectors to be marked bad in this case. This procedure should only be used to restore known bad sector information which was destroyed.

It is no longer necessary to reboot to allow the kernel to reread the bad-sector table from the drive.

SEE ALSO
badsect(8)

HISTORY
The bad144 command appeared in 4.1BSD.

BUGS
It should be possible to format disks on-line under 4BSD.

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

On an 11/750, the standard bootstrap drivers used to boot the system do not understand bad sectors, handle ECC errors, or the special SSE (skip sector) errors of RM80-type disks. This means that none of these errors can occur when reading the file /netbsd to boot. Sectors 0-15 of the disk drive must also not have any of these errors.

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.