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From: clp@mips.com (Carol Preston)
Newsgroups: comp.sys.mips
Subject: Re: bad block tables lost?
Message-ID: <3670@spim.mips.COM>
Date: 20 May 91 05:12:27 GMT
References: <91May16.033557edt.18604@me.utoronto.ca>
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SCSI and SMD keep track of defects differently.  SCSI keeps track of the 
defect list itself, and SMD basically requires the OS to keep track of 
the list.

For a SCSI disk, the defects that the manufacturer mapped out are kept in
the "primary" defect list.  This can't change.  Those defects that are mapped
out subsequently are put in a "secondary" list.  There is a specific SCSI
command to access the part of the disk where the lists are kept, and the
format command doesn't supply this functionality, for better or worse.

For SMD disks, RISC/os keeps the list of defects and the manner in which
they were mapped, in the volume header (partition 8).  If you re-format this
partition, and don't write out the volume header before exiting the format
program, the list is forever lost and must be reentered.  There are also other
ways in which this list can be lost.  As previously mentioned, one way is
if the block to which they are written goes bad (and can't be recovered).
An on-line format program has been released since RISC/os 4.52, and with it 
comes the functionality for saving the defect list to a Unix file.  I would 
suggest that if you are worried about losing this list, you should run 
/etc/format, and do nothing more than list the defects to a file.  (Of 
course, I would not recommend keeping this file on the same disk.)

Additionally '/etc/badspots -l' displays the defect list for a given disk.  
For SCSI, it lists both the primary and secondary lists, and for SMD, it 
lists the defects stored in the volume header.

Both format and badspots have a man page with further information.  Neither
of these commands can be run on pre-4.52 kernels as they use newly defined
ioctl calls.
-- 
Carol Preston
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