bad144 - read/write DEC standard 144 bad sector information
bad144 [-c] [-n] [-v] disk [snum [bad ...]]
bad144 -a [-c] [-n] [-v] disk [bad ...]
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 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
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 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 {
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 putatively
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.
badsect(8)
The bad144 command appeared in 4.1BSD.
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.
OpenBSD 3.6 June 6, 1993
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