Add info for bad block remapping on ESDI drives.

Submitted by:	 Ted Mittelstaedt <tedm@toybox.placo.com>

FAQ/troubleshoot.sgml

@@ -1,4 +1,4 @@
-<!-- $Id: troubleshoot.sgml,v 1.5 1998-06-27 01:13:49 hoek Exp $ -->
+<!-- $Id: troubleshoot.sgml,v 1.6 1998-11-18 21:40:32 dwhite Exp $ -->
 <!-- The FreeBSD Documentation Project -->
 
   <sect>
@@ -25,23 +25,72 @@
         ARRE (Auto Read Reallocation Enbld):  1
       </verb>
 
-      <p>For other drive types, you are dependent on support from the
+      <p>The following paragrahs were submitted by 
-      operating system.  Unfortunately, the ``bad144'' command that
+      <url url="mailto:tedm@toybox.placo.com" name="Ted Mittelstaedt">:
-      FreeBSD supplies for this purpose needs a considerable amount
-      of work done on it. In other words, it doesn't work. If you're
-      lucky, you can create a file that contains the bad blocks and
-      stuff it away with a name like ".BADBLOCKS". This is how I got
-      386BSD Patchkit 24 completed. <tt/NOTE/: don't do this unless
-      your time is effectively free.
 
-      <p>IDE drives are <em/supposed/ to come with built-in bad-block
+      <p>For IDE drives, any bad block is usually a sign of potential trouble.
-      remapping; if you have documentation for your drive, you may want
+      All modern IDE drives come with internal bad-block remapping turned 
-      to see if this feature has been disabled on your drive.  However,
+      on.  All IDE hard drive manufacturers today offer extensive 
-      ESDI, RLL, and ST-506 drives normally do not do this.
+      warranties and will replace drives with bad blocks on them.
 
-      <p>If remapping is enabled and you are seeing bad blocks, consider
+      <p>If you still want to attempt to rescue an IDE drive with bad blocks,
-      replacing the drive.  The bad blocks will only get worse as time
+      you can attempt to download the IDE drive manufacturer's IDE diagnostic 
-      goes on.
+      program, and run this against the drive.  Sometimes these programs can 
+      be set to force the drive electronics to rescan the drive for bad blocks 
+      and lock them out.
+
+      <p>For ESDI, RLL and MFM drives, bad blocks are a normal part of the 
+      drive and are no sign of trouble, generally.  With a PC, the disk drive 
+      controller card and BIOS handle the task of locking out bad sectors.  
+      This is fine for operating systems like DOS that use BIOS code to 
+      access the disk.  However, FreeBSD's disk driver does not go through 
+      BIOS, therefore a mechanism, bad144, exists that replaces this 
+      functionality.  bad144 only works with the wd driver,
+      it is NOT able to be used with SCSI.  bad144 works by entering all bad
+      sectors found into a special file.
+
+      <p>One caveat with bad144 - the bad block special file is placed on the 
+      last track of the disk.  As this file may possibly contain a listing for
+      a bad sector that would occur near the beginning of the disk, where the 
+      /kernel file might be located, it therefore must be accessible to the 
+      bootstrap program that uses BIOS calls to read the kernel file.  This 
+      means that the disk with bad144 used on it must not exceed 1024 
+      cylinders, 16 heads, and 63 sectors.  This places an effective limit 
+      of 500MB on a disk that is mapped with bad144.
+
+      <p>To use bad144, simply set the "Bad Block" scanning to ON in the 
+      FreeBSD fdisk screen during the initial install.  This works up through 
+      FreeBSD 2.2.7. The disk must have less than 1024 cylinders.  It is 
+      generally recommended that the disk drive has been in operation for at 
+      least 4 hours prior to this to allow for thermal expansion and track 
+      wandering.
+
+      <p>If the disk has more than 1024 cylinders (such as a large ESDI drive)
+      the ESDI controller uses a special translation mode to make it work 
+      under DOS. The wd driver understands about these translation modes, 
+      IF you enter the "translated" geometry with the "set geometry" command 
+      in fdisk.  You must also NOT use the "dangerously dedicated" mode of 
+      creating the FreeBSD partition, as this ignores the geometry.  Also, 
+      even though fdisk will use your overridden geometry, it still knows the 
+      true size of the disk, and will attempt to create a too large FreeBSD 
+      partition.  If the disk geometry is changed to the translated geometry, 
+      the partition MUST be manually created with the number of blocks.
+
+      <p>A quick trick to use is to set up the large ESDI disk with the ESDI 
+      controller, boot it with a DOS disk and format it with a DOS partition.
+      Then, boot the FreeBSD install and in the fdisk screen, read off and 
+      write down the blocksize and block numbers for the DOS partition.  Then, 
+      reset the geometry to the same that DOS uses, delete the DOS partition, 
+      and create a "cooperative" FreeBSD partition using the blocksize you 
+      recorded earlier.  Then, set the partition bootable and turn on bad 
+      block scanning.  During the actual install, bad144 will run first, 
+      before any filesystems are created.  (you can view this with an Alt-F2)  
+      If it has any trouble creating the badsector file, you have set too 
+      large a disk geometry - reboot the system and start all over again  
+      (including repartitioning and reformatting with DOS).
+
+      <p>If remapping is enabled and you are seeing bad blocks, consider 
+      replacing the drive. The bad blocks will only get worse as time goes on.
 
     <sect1>
       <heading>FreeBSD does not recognize my Bustek 742a EISA SCSI!</heading>