Dan Nelson wrote:

In the last episode (Aug 06), Gary Corcoran said:

Mike Meyer wrote:


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.

Gary

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