# 2.11BSD#431 - /usr/man/cat8/bad144.0

    BAD144(8)	    UNIX Programmer's Manual		BAD144(8)

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

    SYNOPSIS
         bad144 disktype disk [ sno [ bad ...  ] ]

    DESCRIPTION
         Bad144 can be used to inspect the information stored on a
         disk that is used by the disk drivers to implement bad sec-
         tor forwarding.  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.  Only the first of these copies is
         used.

         Replacement sectors are allocated starting with the first
         sector before the bad sector information and working back-
         wards towards the beginning of the disk.  A maximum of 126
         bad sectors can be supported.  The position of the bad sec-
         tor in the bad sector table determines which replacement
         sector it corresponds to.

         The bad sector information and replacement sectors are con-
         ventionally only accessible through the ``h'' 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[MAXBAD];
         };

         Unused slots in the bt_bad array are filled with all bits
         set, a putatively illegal value.  MAXBAD (in <sys/dkbad.h>)
         may be tuned locally to reduce the space required to hold
         the bad-sector file in memory.  It may not be greater than
         126, which uses the whole disk sector.  Bad sectors past
         MAXBAD may be included by the formatter, but replacement
         sectors will not be used until MAXBAD is increased.

    Printed 11/26/99						1

    BAD144(8)	    UNIX Programmer's Manual		BAD144(8)

         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 correspond-
         ing 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 infor-
         mation onto the same location.  Note, however, that 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.

         New bad sectors can be added by running the standard DEC
         formatter in section ``bad.''

    SEE ALSO
         badsect(8)

    BUGS
         Not all drivers support bad-sector forwarding on the PDP-11.

         It should be possible to both format disks on-line under
         UNIX and to change the bad sector information, marking new
         bad sectors, without running a standalone program.

         The bootstrap drivers used to boot the system do not under-
         stand bad sectors or handle ECC errors.  This means that
         none of these errors can occur when reading the file /unix
         to boot.  Sector 0 of the disk drive and the file /boot in
         the root file system of that drive must also not have any of
         these errors in it.

         The drivers that 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.

    Printed 11/26/99						2

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