BAD144(8) BSD System Manager's Manual BAD144(8)NAME
bad144 - read/write DEC standard 144 bad sector information
SYNOPSIS
bad144 [-c] [-n] [-v] disk [snum [bad ...]]
bad144 -a [-c] [-n] [-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 options are as follows:
-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 be 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.
-n Make no permanent changes. Useful for debugging. Implies -v.
-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 fol-
lows. 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 disk.o. 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 replace-
ment 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 {
long bt_csn; /* cartridge serial number */
u_short bt_mbz; /* unused; should be 0 */
u_short bt_flag; /* -1 => alignment cartridge */
struct bt_bad {
u_short bt_cyl; /* bad sector cylinder number */
u_short bt_trksec; /* track and sector number */
} bt_bad[126];
};
Unused slots in the bt_bad array are filled with all bits set, a puta-
tively illegal value.
bad144 is invoked by giving a device name (e.g., "hk0", "hp1"). 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 ALSObadsect(8)HISTORY
The bad144 command appeared in 4.1BSD.
BUGS
It should be possible to format disks on-line under UNIX.
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 /bsd 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.
MirOS BSD #10-current June 6, 1993 1
