Disk block or sector to file mapping?

Peter Jeremy peterjeremy at optushome.com.au
Fri Jun 15 11:50:23 UTC 2007


On 2007-Jun-13 21:08:48 -0700, Jeremy Chadwick <koitsu at freebsd.org> wrote:
>Realistically, what we need on FreeBSD is a tool similar to Solaris's
>format(8) "analyze" command, which does a raw disk scan (r, r/w, and a
>couple other operations).

The "analyze" function is just a pattern test with the ability to
restore the original content.  Writing one is trivial.

>[1] - If the OS is seeing bad blocks on a PATA/SATA disk, usually it means
>that the internal remapping table is full, which means that there were
>other bad blocks on the disk which it has silently remapped for you to
>avoid pain -- and space for those blocks has been exhausted.

Re-mapping generally only works on writes.  If you can't read existing
data off the platter then you will get a bad block error irrespective
of the remapping table.  A sector that could not be read can often be
written.

>and you're stuck simply replacing the disk entirely.  Bad blocks have a
>tendency to spread too...

Definitely - once the number of soft errors starts increasing, it's
time to replace the disk.

-- 
Peter Jeremy
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