Is a disk image created within dd "safe"?

[Clint Olsen]

Hi:

I currently use Cygwin and rsync to provide Time Machine-like
functionality to a NAS on my home network. This works fine for user
data.

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?

A friend speculated that dd might complain about open files or
some-such thing. I went and tried it on /dev/sda and it seemed to work
without complaining.

Example:

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

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.

Thanks,

-Clint

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