Subject: Re: Bad Blocks
To: None <, tih@Hamartun.Priv.NO>
From: Johnny Billquist konsult <>
List: port-vax
Date: 04/26/1996 10:59:13
> | There are no working bad block replacement system on MSCP disks,
> | and I have no idea about how it should work (I have no docs on
> | the MSCP protocol). What should work anyway is the program badsect;
> | which creates a file of the bad blocks mentioned. Try that.
> As a temporary solution, maybe.  However, bad blocks are not supposed
> to be an issue with MSCP disks; the controller is supposed to hide
> such evil from the rest of the system.  This even holds for RX50
> floppies, actually.  :-)  The Right Thing when an MSCP disk shows up
> bad spots would be to use badsect(8) to trap them until a reformat can
> be performed.  (I don't believe MSCP controllers can dynamically remap
> bad blocks, in general.)

As a matter of fact, MSCP controllers can dynamically remap bad
blocks, it's just that Unixes (apart from Ultrix) don't know how
to tell the controller to remap a block going bad.
All DEC OSes I know of remaps bad blocks.

And now a *big* warning.

*Don't* reformat drives unless you absolutely have to. You can turn
the drive useless by doing that.

If you are running NetBSD or whatever, and are having lots of
bad spots you want to go away, use the diagnostic utility for
remapping bad blocks instead. EVRLK unless my memory fails me.

So, you ask yourself, how can the disk become useless by reformatting?
Well, if the format program decides the disk is too bad, it refuses
to complete the format. However, when the format starts, some information
is recorded to tell that the disk isn't proprely formatted, so any attempt
to bring the disk online will fail.

By just remapping bad blocks, you can keep the drive working just fine, even
though format would regard the disk as hopelessly corrupted.