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BAD144(8)                   System Manager's Manual                  BAD144(8)



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

SYNOPSIS
       /etc/bad144 [ -f ] 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 sector forwarding.  The  for-
       mat of the information is specified by DEC standard 144, as follows.

       The bad sector information is located in the first 5 even numbered sec-
       tors 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, a  puta-
       tively illegal value.

       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 sup-
       plied information 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.  It is necessary 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''.  NOTE:
       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 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.

SEE ALSO
       badsect(8), format(8V)

BUGS
       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 /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.



4th Berkeley Distribution        18 July 1983                        BAD144(8)