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Date:	Tue, 23 Jun 2020 10:06:25 -0600
Message-ID:	<CAKNeuBqZpacuUwTD6U+kKPGOO052VYhpRnttm=HYr7m+OT7tiA@mail.gmail.com>
Subject:	Re: [cygwin] DD bug fails to wipe last 48 sectors of a disk
To:	cygwin <cygwin AT cygwin DOT com>
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From:	Nicholas Clark via Cygwin <cygwin AT cygwin DOT com>
Reply-To:	Nicholas Clark <nicholas DOT clark AT gmail DOT com>
Sender:	"Cygwin" <cygwin-bounces AT cygwin DOT com>

Do you get the same behavior when you run dd with iflag=fullblock? Without
that flag, it's possible dd's input to read a smaller block than requested
(which would correspond with a smaller write to the output).

On Tue, Jun 23, 2020 at 9:28 AM Hashim Aziz via Cygwin <cygwin AT cygwin DOT com>
wrote:

> I hadn't checked with 512 byte block sizes because of the amount of time
> it would have taken, but sure enough have just finished trying with bs=512
> and no block size at all (so dd's default block size, which is either 512
> or 1024) and although each wipe took over 24 hours, they did indeed wipe
> all of the sectors. So it seems that there's a bug with regards to how
> Cygwin handles the last block when a large (i.e. sane) block size is
> selected, and that this bug doesn't occur on actual UNIX-based systems.
>
> ________________________________
> From: Cygwin <cygwin-bounces AT cygwin DOT com> on behalf of Eliot Moss <
> moss AT cs DOT umass DOT edu>
> Sent: 20 June 2020 9:26 PM
> To: The Cygwin Mailing List <cygwin AT cygwin DOT com>
> Subject: Re: [cygwin] DD bug fails to wipe last 48 sectors of a disk
>
> On 6/20/2020 1:31 PM, Hashim Aziz via Cygwin wrote:
> > To reproduce simply run the following command on a drive (obviously,
> this will irreversibly wipe all data):
> >
> > dd if=/dev/zero of=/dev/sdX bs=4M status=progress
> >
> > Both drives were attached via internal SATA (by way of a PCIE to SATA
> Host Bus Adapter).
> >
> > Cygwin was running in an elevated window as dd cannot run in Cygwin
> without administrator access, at least not on Windows 10 and not when
> dealing with raw disks. I was running Avast the first time I discovered
> this, and am currently running Windows Defender, so doubt that the AV is
> the cause of this.
> >
> > The hard drives are a Western Digital WD10PURX-64E5EY0 (Serial:
> WD-WCC4J6HX189U) and a Kingston SV200S3128G (Serial: 12BA315PKAWK).
> >
> > I just ran DD for Windows 0.6beta3 with variations of the following
> command:
> >
> > dd.exe if=/dev/zero of=\\.\PHYSICALDRIVEX --progress bs=4M
> >
> > ...and can confirm that the bug also manifests here, but in a slightly
> different way - irrespective of the disk or block size, it fails to wipe
> the last 176 sectors of the drive.
>
> I was going to ask: even with block size 512 bytes?  But I guess you
> checked that ...
>
> Regards - Eliot
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