+.TH BAD144 8 "18 July 1983"
+.UC 4
+.SH NAME
+bad144 \- read/write dec standard 144 bad sector information
+.SH SYNOPSIS
+.B /etc/bad144
+[
+.B \-f
+]
+disktype disk
+[ sno [
+bad ...
+] ]
+.SH DESCRIPTION
+.I 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 follows.
+.PP
+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
+.I dkbad
+structure.
+.PP
+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.
+.PP
+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.
+.PP
+The bad sector structure is as follows:
+.PP
+.ta .75i 1.5i 3.5i
+.nf
+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];
+};
+.fi
+.PP
+Unused slots in the
+.I bt_bad
+array are filled with all bits set, a putatively
+illegal value.
+.PP
+.I Bad144
+is invoked by giving a device type (e.g. rk07, rm03, rm05, etc.), and a device
+name (e.g. hk0, hp1, 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
+.I 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.
+.PP
+If the disk is an RP06, Fujitsu Eagle,
+or Ampex Capricorn on a Massbus, the
+.B \-f
+option may be used to mark the bad sectors as ``bad''.
+\fBNOTE: this can only be done safely when there is no other disk activity\fP,
+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.
+.SH SEE ALSO
+badsect(8),
+format(8V)
+.SH BUGS
+It should be possible to format disks on-line under UNIX.
+.PP
+It should be possible to mark bad sectors on drives of all type.
+.PP
+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.
+.PP
+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.
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