Questions[zero-fill](server)

A client sent us an external hard drive where at least half the files are corrupt. They are broad mix of filetypes (images, documents, etc) and there is no discernible pattern into which are corrupt. They appear as their original size, however, when I open them in a hexeditor they are filled with nothing but nulls. The data has been completely replaced with 00s.

What could cause this to happen? The files were likely copied onto the drive from another machine. Could this result from problems during a transfer or is it more likely the files are corrupt at the origin?

I am trying to use the windows version of dd to copy a RHEL iso to a USB stick. However, I wanted to zero out the drive first to ensure there is no filesystem on it before writing it out. Is there an equivalent of /dev/zero in windows that I can use as the infile?

How to zero fill a virtual disk's free space on windows for better compression?

I would like a simple open source tool (or at least free) for that. It should probably write an as big as possible file full of 0and erase it afterwards. Only one pass (this is not for security reasons but for compression, we are backing up virtual machines).

Should run from inside windows and not from a disk.

On Linux I do it like this (as a user):

cd
mkdir wipe
sudo sfill -f -l -l -z ./wipe/

Edit 1: I decided to use sdelete from the accepted answer. I had a look at the sdelete's help:

C:\WINDOWS\system32>sdelete /?

SDelete - Secure Delete v1.51
Copyright (C) 1999-2005 Mark Russinovich
Sysinternals - www.sysinternals.com

usage: sdelete [-p passes] [-s] [-q] <file or directory>
       sdelete [-p passes] [-z|-c] [drive letter]
   -c         Zero free space (good for virtual disk optimization)
   -p passes  Specifies number of overwrite passes (default is 1)
   -q         Don't print errors (Quiet)
   -s         Recurse subdirectories
   -z         Clean free space

This is an old version. I used the -c switch from the 2nd invocation and this was quite fast (syntax only valid for older versions before V1.6):

c:\>sdelete -c c: (OUTDATED!)

I have the impression this does what I want. The sdelete tool is easy to use and easy to get.

Edit 2: As scottbb pointed out in his answer below, there was a September 2011 change to the tool (version 1.6) The -c and -z options have changed meanings. The correct usage from 1.6 onwards is

c:\>sdelete -z c:

Edit 3: There is a 2.0 version of sdelete and sdelete64. They appear to be buggy when zeroing. It will appear to be stuck at 100% for extremely long times. Some people have reported 10 - 40 times longer. The older version 1.61 does not have this issue. See https://social.technet.microsoft.com/Forums/en-US/2ffb2539-34ba-4378-aa8a-941d243f117e/sdelete-hangs-at-100?forum=miscutils

Edit 4: Now there's the issue of dynamically allocated virtual disc space. If you have a 100GB disk that is not full and uses only 30GB on the host, zero filling should not increase dramatically the size of the disc because that contradicts the purpose of dynamic allocation. There is an answer for Oracle VM VirtualBox https://superuser.com/q/907196/44402 - but on other stacks like VMWare, Xen, XenServer, etc., this needs to be answered separately.

I'm attempting to zero a disk on my Mac OS X machine. I'm going for complete zeros and unformatted, so I think of dd. Unfortunately the maximum throughput I've managed to get out of dd is 7MB/s. Just for grins I tried disk utility and it has a throughput of 19MB/s. What gives? I've tried changing the bs option on dd to all sorts of values, but it still hovers around 7MB/s. Why is disk utility so much faster?

What is the best and fastest wipe drive (zero fill) utility that can be burned to a CD?