tool for mapping away bad blocks on an external disk

Polytropon freebsd at
Sun Apr 17 17:40:06 UTC 2016

On Sun, 17 Apr 2016 13:28:03 -0400, 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.

This was also possible with PATA ("IDE") disks and a PC BIOS that
had the feature "media analysis" and "low level format". Additionally,
when you could locate the position of the damaged blocks, you could
"format the disk smaller" by changing some of the CHS values - the
disk became smaller, and the defective sectors outside of its new
geometry weren't touched anymore. I remember having dealt with a
faulty 80 MB disk, reformatted to 40 MB, which didn't show any kind
of problems afterwards, for years. This was when hard disks were
expensive and low level access was possible. :-)

> The old Adaptec 1540 and 2940 controllers come to mind (Ctrl-A to 
> enter the controller BIOS during POST).

Yes, the 2940s had this feature.

> Can't do this through a USB subsystem.

Result of "making easy things hard, and clever things impossible"... :-)

Magdeburg, Germany
Happy FreeBSD user since 4.0
Andra moi ennepe, Mousa, ...

More information about the freebsd-questions mailing list