Destroying data down to the 13th level??? Post: 18920

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Special Forums Hardware Filesystems, Disks and Memory Destroying data down to the 13th level??? Post 18920 by Perderabo on Thursday 4th of April 2002 08:17:40 AM

04-04-2002

Administrator Emeritus

Quote:

Originally posted by LivinFree
I know it would be taxing on the disk, and possibly the entire system, but for curiosity sake, would it work?

I am not sure of what urandom is, so I must pass on that. Using dd to copy /dev/zero to a disk special file will work in all cases if you use the default block sizes as you are doing.

You don't specify whether you are using a block special file or a character special file to access the disk. That cat would be expensive but would work if you use a block special file.

It is not guaranteed to work if you use a character special file, but it might depending on the disk driver, the disk hardware, and block size used for physical writes by the cat command. A raw disk device requires i/o to be aligned on a DEV_BSIZE boundary. But it's not guaranteed to fail if you don't do that.

The second smartest way to do this would be to use dd to copy /dev/zero to the raw device but using a very large block size that is a multiple of DEV_BSIZE.

But HP-UX has mediainit and SunOS has format. Instead of zeros on every pass, they use various patterns chosen by hardware experts to really test the disk. If you need more security than that, you need to use sledge hammers and blow torches.

Perderabo

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LEARN ABOUT PLAN9

wren

WREN(3) 						     Library Functions Manual							   WREN(3)

NAME

       wren, ata - hard disk interface

SYNOPSIS

       bind #H[drive] /dev
       bind #w[target[.lun]] /dev

       /dev/hd0disk
       /dev/hd0partition
       /dev/sd0disk
       /dev/sd0partition
	...

DESCRIPTION

       The  hard  disk interfaces (wren, #w, is a SCSI disk; ata, #H, is an IDE or ATA disk) serve a one-level directory giving access to the hard
       disk partitions.  The parameter to attach defines the numerical SCSI target and logical unit number or the  IDE	drive  number  to  access.
       Both default to zero.

       Each  partition name is prefixed by hd and the numeric drive identifier.  The partition always exists and covers the entire disk.  The size
       of each partition as reported by stat(2) is the number of bytes in the partition, so the size of is the size of the entire disk.

       The partition also always exists; it is the last block on the disk for SCSI, second to last for IDE.  If it contains valid partition  data,
       those  partitions will be visible as well.  Every time the device is bound, the partitions are updated to reflect any changes in the parti-
       tion file.

       The format of the partition file is the string

	      plan9 partitions

       on a line, followed by partition specifications, one per line, consisting of a name and textual strings for the block start and	limit  for
       each partition on the disk.

       The program prep(8) writes the partition table for the disk; its use is preferred to writing it by hand.

SEE ALSO

       prep(8), scsi(3)

SOURCE

       /sys/src/9/port/devwren.c
       /sys/src/9/pc/devata.c

																	   WREN(3)