bug in Interactive Fast File System?

[Tony Field]

I am running Interactive 2.2 on a generic 33mHz system with an RLL controller
driving two disks.  Typically, every week or two, the system is unable to
access the second drive.  The following error message is printed during
boot:

	DEVICE ERROR:  Unrecoverable data error in setor.
	               Controller 0 (Primary AT harddisk) disk drive 1
	               Absolute sector #432354
	NOTICE: free block read error on primary AT hard disk
		       unit 1 partition 7

The indicated sector was detected as "bad" during the initial file scan
at system install time. In addition, it is marked as a bad sector 
in /etc/partitions.

Is there any known reason why this should happen?  

It looks as though the in-memory free space list maintained by the FFS is
getting confused and an incorrect free space list is written back to disk
during shutdown.

tony....
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