tool for mapping away bad blocks on an external disk

Warren Block wblock at
Sun Apr 17 17:55:14 UTC 2016

On Sun, 17 Apr 2016, Michael Powell wrote:

> Back in the day  (Fixed Direct Access SCSI-2 device) you could use the
> controller BIOS to do what used to be known as a "low level format" of SCSI
> drives in order to attempt to squeak a little more life from them. And if
> new bad spots did not begin to pop again right away you might be good to go
> for a while. If they did it indicated mass media failure that would just
> avalanche. The old Adaptec 1540 and 2940 controllers come to mind (Ctrl-A to
> enter the controller BIOS during POST).
> Can't do this through a USB subsystem.

Or to pretty much any drive any more.  They will accept the low-level 
format command, but return immediately.  Or that's what happened the 
last time I tried it, years ago.

It's been a long time since hard drives gave any direct access to the 
media.  Everything goes through the controller on the drive now, which 
handles all that transparently.  So blocks that appeared bad might be 
already mapped out by the drive.

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