bad144(8)bad144(8)Namebad144 - read/write DEC Standard 144 bad sector information
Syntax
/etc/bad144 [ -f ] disktype disk [ sno [ bad ... ] ]
Description
The command 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 fol‐
lows.
The bad sector information is located in the first five 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 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 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; /* cylinder number of bad sector */
u_short bt_trksec; /* track and sector number */
} bt_bad[126];
};
Unused slots in the bt_bad array are filled with all bits set, an
accepted illegal value.
The command is invoked by giving a device type (for example, rk07,
rm03, rm05, and so forth), and a device name (for example, hk0, hp1,
and so forth). It reads the first sector of the last track of the cor‐
responding 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 sec‐
tors, and will then write the supplied information onto the same loca‐
tion. Note, however, that 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 neces‐
sary to reboot before the change will take effect.
If the disk is an RP06, Fujitsu Eagle, or Ampex Capricorn on a Massbus,
the -f option may be used to mark the bad sectors as ``bad''. 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 sec‐
tors 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.
Restrictions
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 /vmunix 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.
See Alsobadsect(8), format(8v)
VAX bad144(8)