[CentOS] imaging a drive with dd

[Robert Moskowitz]

On 03/02/2017 08:53 PM, Warren Young wrote:
> On Mar 2, 2017, at 6:36 PM, Robert Moskowitz <rgm at htt-consult.com> wrote:
>> I want to image the drive at various 'checkpoints' so I can go back and redo from a particular point…
>> what dd params work?
>>
>> dd if=/dev/sdb of=os.img bs=1M count=3210
> That looks plausible.  (I haven’t verified your count parameter exactly.)
>
> However, I wonder why you’re trying to reinvent snapshots, a technology now built into several advanced filesystems, such as btrfs and ZFS?
>
>      https://en.wikipedia.org/wiki/Btrfs#Subvolumes_and_snapshots
>
> btrfs is built into CentOS 7.  While there have been some highly-publicized bugs in btrfs, they only affect the RAID-5/6 features.  You don’t need that here, so you should be fine with btrfs.
>
> And if you really distrust btrfs, ZFS is easy enough to integrate into CentOS on-site.
>
> And if *that* is also out of the question, you have LVM2 snapshots:
>
>      http://tldp.org/HOWTO/LVM-HOWTO/snapshots_backup.html
>
> Why reinvent the wheel?

This is Centos7-armv7.  Not all the tools are there.  I keep getting 
surprises in some rpm not in the repo, but if I dig I will find it (but 
php-imap is NOT built yet and that I need).

The base image is a dd, and you start with something like:

xzcat CentOS-Userland-7-armv7hl-Minimal-1611-CubieTruck.img.xz | sudo dd 
of=/dev/sdb bs=4M; sync

btw, this reports:

0+354250 records in
0+354250 records out
3221225472 bytes (3.2 GB, 3.0 GiB) copied, 120.656 s, 26.7 MB/s

Then you boot up (connected via the JART with a USB/TTL for a serial 
console).

I want a drive image, and that is easy to do.  I disconnect my drive 
from the CubieTruck, stick it into a USB/sata adapter, and I can image 
the whole drive.

For just a development and snapshotting project, dd (and xzcat) do the 
job, and really what the Fedora-arm and Centos-arm teams have been doing.

I actually did this 2+ years creating Redsleeve6 images, but can't find 
any of my notes.  :(