Makin' backups -- questions

David Christensen dpchrist at
Sat Jun 13 04:41:38 UTC 2020

On 2020-06-12 17:00, Ronald F. Guilmette wrote:

> But seriously, I have found that copying whole partitions is often easiest
> using the Linux gparted tool. 

I use LUKS, GELI, and ZFS.  Unfortunately, I do not believe gparted nor 
Clonezilla support them:

> DD is quite obviously an -extremely- low
> level tool, and rather ham-fisted.  Clonezilla can also copy individual
> partitions.  Me personally?  I wouldn't use DD except to copy -everything-
> between two drives having exactly the same number of sectors. 

I have an assortment of "16 GB" devices of varying sizes:

2020-06-12 20:58:04 dpchrist at tinkywinky ~/hardware
$ cat `find samsung sandisk/ultra-fit -name fdisk.out` | egrep '14.. 
GiB' | perl -pe 's/.+ (\d+ sectors)/$1/' | sort | uniq
30031872 sectors
30375936 sectors
31266816 sectors
31277232 sectors

When installing, I use 1 MiB + 14 GiB = 29362176 sectors and leave the 
rest as unused space.

When imaging, I copy from sector 0 to the end of the last MBR partition 
(FreeBSD slice).  I can put the image onto any of the above devices, and 
the device will boot and work as a system drive.

> Note that
> if you use DD to copy from a smaller drive to a bigger drive, then afterwards
> the BIOS and everything else will tell you that the destination drive's
> physical size is -smaller- than it actually is, i.e. exactly equal to the
> size of the (smaller) source drive.

I haven't seen that.  I gather drive metadata and check it into CVS 
whenever I wipe a device, do a fresh install, take an image, or restore 
an image. I will pay more attention to 'cvs diff' in the future.

I would be curious to see a demonstration console session.

> Yet another reason not to use DD to copy either whole disks or partitions...
> unless the size of the destination is -exactly- equal to that of the source.

I agree that partition sizes must be identical for dd(1) to produce a 
correct result.

But, I know that device sizes do not need to be identical if you use MBR 
partitioning and leave free space at the end.


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