It was broucht up before indeed: https://lists.samba.org/archive/rsync/2012-June/027680.html

On 12/30/18 9:50 PM, devzero--- via rsync wrote:
There have been addons to rsync in the past to do that but rsync really
isn't the correct tool for the job.
why not correct tool ?

if rsync can greatly keep two large files in sync between source and destination
(using --inplace), why should it (generally spoken) not also be used to keep two
blockdevices in sync ?

maybe these links are interesting in that context:

https://lists.samba.org/archive/rsync/2010-June/025164.html

https://github.com/dop251/diskrsync

roland

Gesendet: Sonntag, 30. Dezember 2018 um 19:53 Uhr
Von: "Kevin Korb via rsync" <rsync@lists.samba.org>
An: rsync@lists.samba.org
Betreff: Re: rsync remote raw block device with --inplace

There have been addons to rsync in the past to do that but rsync really
isn't the correct tool for the job.  Neither is dd.

The right tool is something that understands the filesystem within the
block device such as ntfsclone (what I use) or partimage (if you have
ever used Clonezilla this is what it uses).  These will know how to skip
all the empty parts of the filesystem and will still be capable of
restoring a complete image in a bare metal restore.  You can still use
dd to snag a copy of the MBR since that is outside of any filesystems.

Also, if you do have to resort to a plain image use ddrescue instead of
dd.  It has a status screen and it can resume as long as you used a log
file when you ran it.

On 12/30/18 1:45 PM, Steve Newcomb via rsync wrote:
It would be very nice to be able to rsync the raw data content of, e.g.,
a non-mounted disk partition, particularly in combination with --inplace.

Our reality: several dual-boot machines running Windows during the day
and Linux at night, during backups.  Windows is very tedious and iffy to
re-reinstall without a raw disk image to start from.  Disks fail, and
the ensuing downtime must be minimized.

We're using dd for this.  Most of the nightly work is redundant and
wasteful of elapsed time and storage.  Storage is cheap, but it's not
*that* cheap.  Elapsed time is priceless.

Rsync refuses to back up raw devices, and even raw character devices,
with the message "skipping non-regular file" (I think the relevant
message is in generator.c).

In Linux, anyway, the "raw" command allows a block device to be bound as
a character device, and then even a "cat" command can read the raw data
of the block device.  So why does rsync refuse to copy such content, or
why is it a bad idea, or what rsync doctrine conflicts with it?  I agree
there are security concerns here, but rsync already disallows some of
its functions unless the super user is requesting them.


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