2.11BSD/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
     _B_a_d_1_4_4 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)



     _B_a_d_1_4_4 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 _b_a_d_1_4_4
     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