it was said:

> > >>>Modern drives deal with bad block substitution
all by themselves.
> > >>
> > >>Umm - not quite, right?  That is, if a block
"goes bad" and you get a
> > >>read error, the drive isn't going to do any
"substituting" at that
> > >>point.  You'll just continue to get the read
error if you try to
> > >>access (read) that block.  It's only when you
allow another *write*
> > >>to that block (e.g. by deleting the original
file and writing new
> > >>files) that the drive will automatically
substitute a spare block for
> > >>the one that went bad.
> > >
> > >
> > >SCSI drives, at least, may do automatic
reallocation on both reads and
> > >writes ( camcontrol mode da0 -m 1, the ARRE and
AWRE flags ).  If the
> > >drive had to reread the block or had to use ECC
to recover data, AND
> > >the entire block was recovered, it will relocate
the data if ARRE is
> > >set.
> > 
> > Good to know, although I stopped buying SCSI disks
(for home use)
> > years ago.  I presumed the more common case these
days, that we
> > were talking about IDE disks.  In fact doesn't
this (from the original
> > question):
> > 
> > ad0s1a: hard error
> > 
> > necessarily refer to an ATA (IDE) disk?  I don't
believe any (current)
> > ATA disks will do automatic reallocation on reads,
will they?  Though
> > of course serial ATA drives seem to be "the
future" and are taking
> > on more and more SCSI-like features as time goes
by.
> 
> Both ATA and SCSI drives may relocate blocks that
were difficult
> to read (e.g. correctable errors, took multiple
attempts, etc).
> But if the block can't be recovered at all, the
drive will still
> report an error to the OS (in addition to
relocation).

Hello,

A tool that all may find useful is SpinRite 6.0
available from Gibson Research at
http://www.grc.com/sr/spinrite.htm. It's not open
source or freeware but anybody with an Intel, AMD, or
TiVO system that uses a harddrive ought to have it.
Note: I am in no way affiliated with Gibson Research,
other than having used SpinRite since the days of
manually interleaving MFM drives.

HTH,

Stheg


                
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