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bad144(8) [bsd man page]

BAD144(8)						      System Manager'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 sector 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 backwards towards the begin- ning of the disk. A maximum of 126 bad sectors can be supported. The position of the bad sector in the bad sector table determines which replacement sector it corresponds to. The bad sector information and replacement sectors are conventionally 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. 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 sec- tor 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 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 understand 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. 3rd Berkeley Distribution BAD144(8)

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BADSECT(8)						    BSD System Manager's Manual 						BADSECT(8)

NAME
badsect -- create files to contain bad sectors SYNOPSIS
badsect bbdir sector ... DESCRIPTION
badsect makes a file to contain a bad sector. Normally, bad sectors are made inaccessible by the standard formatter, which provides a for- warding table for bad sectors to the driver; see bad144(8) for details. If a driver supports the bad blocking standard it is much preferable to use that method to isolate bad blocks, since the bad block forwarding makes the pack appear perfect, and such packs can then be copied with dd(1). The technique used by this program is also less general than bad block forwarding, as badsect can't make amends for bad blocks in the i-list of file systems or in swap areas. On some disks, adding a sector which is suddenly bad to the bad sector table currently requires the running of the standard DEC formatter. Thus to deal with a newly bad block or on disks where the drivers do not support the bad-blocking standard badsect may be used to good effect. badsect is used on a quiet file system in the following way: First mount the file system, and change to its root directory. Make a directory BAD there. Run badsect giving as argument the BAD directory followed by all the bad sectors you wish to add. The sector numbers must be relative to the beginning of the file system, but this is not hard as the system reports relative sector numbers in its console error mes- sages. Then change back to the root directory, unmount the file system and run fsck(8) on the file system. The bad sectors should show up in two files or in the bad sector files and the free list. Have fsck(8) remove files containing the offending bad sectors, but do not have it remove the BAD/nnnnn files. This will leave the bad sectors in only the BAD files. badsect works by giving the specified sector numbers in a mknod(2) system call, creating an illegal file whose first block address is the block containing bad sector and whose name is the bad sector number. When it is discovered by fsck(8) it will ask ``HOLD BAD BLOCK ?'' A positive response will cause fsck(8) to convert the inode to a regular file containing the bad block. DIAGNOSTICS
badsect refuses to attach a block that resides in a critical area or is out of range of the file system. A warning is issued if the block is already in use. SEE ALSO
bad144(8), fsck(8) HISTORY
The badsect command appeared in 4.1BSD. BUGS
If more than one of the sectors in a file system fragment are bad, you should specify only one of them to badsect, as the blocks in the bad sector files actually cover all the sectors in a file system fragment. BSD
June 5, 1993 BSD

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