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Special Forums Hardware Filesystems, Disks and Memory Erasing hard disk contents using dd or dcfldd Post 302323126 by jake24 on Friday 5th of June 2009 01:02:54 PM
Old 06-05-2009
Thanks everyone for the responses.
Actually my doubt is if I am doing 2 swipes over the disk with a pattern and its compliment, using either dd/dcfldd for the purpose in a script, then the first swipe should have actually ended up physically on the sectors on disk before the second swipe.
With the script I have pasted in my first post, is the sync in between 2 swipes sufficient to ensure that?
Can anyone help me with some pointers on the impact of OS/disk caches on the way to disk sectors?
 

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disktab(5)							File Formats Manual							disktab(5)

Name
       disktab - disk description file

Syntax
       #include <disktab.h>

Description
       The file is a simple data base that describes disk geometries and disk partition characteristics.  The format is patterned after the termi-
       nal data base.  Entries in consist of a number of fields separated by colons (:).  The first entry for each disk gives the names  that  are
       known for the disk, separated by vertical bars (|).  The last name given should be a long name fully identifying the disk.

       The following list indicates the normal values stored for each disk entry:
       Name Type Description
       ns   num  Number of sectors per track
       nt   num  Number of tracks per cylinder
       nc   num  Total number of cylinders on the disk
       ba   num  Block size for partition `a' (bytes)
       bd   num  Block size for partition `d' (bytes)
       be   num  Block size for partition `e' (bytes)
       bf   num  Block size for partition `f' (bytes)
       bg   num  Block size for partition `g' (bytes)
       bh   num  Block size for partition `h' (bytes)
       fa   num  Fragment size for partition `a' (bytes)
       fd   num  Fragment size for partition `d' (bytes)
       fe   num  Fragment size for partition `e' (bytes)
       ff   num  Fragment size for partition `f' (bytes)
       fg   num  Fragment size for partition `g' (bytes)
       fh   num  Fragment size for partition `h' (bytes)
       pa   num  Size of partition `a' in sectors
       pb   num  Size of partition `b' in sectors
       pc   num  Size of partition `c' in sectors
       pd   num  Size of partition `d' in sectors
       pe   num  Size of partition `e' in sectors
       pf   num  Size of partition `f' in sectors
       pg   num  Size of partition `g' in sectors
       ph   num  Size of partition `h' in sectors
       se   num  Sector size in bytes
       ty   str  Type of disk (e.g. removable, winchester)

       The entries can be automatically generated with the program.

Files
See Also
       chpt(8), newfs(8)

																	disktab(5)
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