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Date: Thu, 3 Sep 2015 05:19:15 +0300
From: Andrey Repin <anrdaemon AT yandex DOT ru>
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Message-ID: <122670706.20150903051915@yandex.ru>
To: Clint Olsen <clint DOT olsen AT gmail DOT com>, cygwin AT cygwin DOT com
Subject: Re: Is a disk image created within dd "safe"?
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Greetings, Clint Olsen!

> I'm also interested in generating images to preserve the entire disk.
> What I'm wondering is whether doing this on a live system through
> Cygwin would produce a safe, bootable disk image or if the the APIs
> that Cygwin has to use or having the disk mounted would make this
> unreliable?

Bootable? Likely.
Safe? not even in the slightest.
And as Eric pointed out, this has nothing to do with Cygwin.

> A friend speculated that dd might complain about open files or
> some-such thing.

You don't have files on a block device level. >.< Tell your friend to
speculate something better.

> I went and tried it on /dev/sda and it seemed to work
> without complaining.

With conv=noerror ?
I'm wondering, what did you expect?

> Example:

> $ dd if=/dev/sda of=/path/to/NAS/sda.img bs=512 conv=noerror,sync

bs=4k at least.
NTFS uses 4k clusters by default, there's no reason to use smaller chunks to
read it.
Actually, even bigger chunks may greatly speed up the read.

conv is just bogus. You are trying to create a mess of the image with these
options.
You don't want any padding.
You don't want errors ignored.

Writing disk image to NAS uncompressed is even more questionable.
Consider piping it through some archiver.

> It would be great if something like this would work since dd is so
> ubiquitous that I could restore a drive in a number of ways and not
> lock me into something proprietary.

It wouldn't work. Not directly. For a number of reasons.
If you still intend to do it, at the very least consider using ERUNT for
registry snapshots. That will let you have a consistent registry copy even if
the one in image would turn up damaged.


-- 
With best regards,
Andrey Repin
Thursday, September 3, 2015 04:50:29

Sorry for my terrible english...


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