wipe /dev/sda

[Kent Borg]

Neil Aggarwal wrote :
> Yes, but unless he has the secret recipe to diet Coke, overwriting
> disk 8 or more times with random data is good enough. That is what
> DBAN recommends for good security.

Heck, writing once is good enough unless someone is *really* interested
in your old data.

However, there other things to worry about: bad sectors.  These days
disks will automatically remap bad sectors, replacing them with spares. 
The bad sectors will still be there and that partial data will likely be
mostly complete.  If all your data is credit card numbers, then even a
little leaking is bad.  If most of your data is uninteresting, then a
small percent slipping into bad sectors is of little risk.  Overwriting
once or a zillion times won't touch data the disk is pretending isn't
there: the bad sectors.  But again, getting at this data (interesting or
not) will require someone who is rather interested in getting at any
scrap of your data that s/he can possibly find.

In summary you really only have three choices:

 - Most secure: physically destroying the disk platter surfaces. 
(Appropriate if you have powerful enemies.)

 - Pretty dang secure: any sort of overwriting that touches all of the
available portions of your disk.  (Appropriate if you expect only
opportunistic foes.)

 - Insecure: reformatting.  (Appropriate if you have no data you care
about keeping secret.)


If you are paranoid enough to spend time on this consider the security
of your data before you are done with your disks.  Do you do regular
backups?  Are the backups encrypted?  Is your working data encrypted? 
Do you regularly wipe your old files by filling the "unused" portions of
your working disk with random data?


-kb