Makin' backups -- questions

[David Christensen]

On 2020-06-12 13:58, Ronald F. Guilmette wrote:
> In message <6ba3f007-3045-99be-5d35-10c75b37ab17 at holgerdanske.com>,
> David Christensen <dpchrist at holgerdanske.com> wrote:
> 
>>>> 2.  I use MBR partitioning, to avoid problems with the GPT backup
>>>> partition table when the source and target device sizes differ.

>>> You're going to have to explain that one to me.  What are these "problems"
>>> of what you speak?
>>
>> See "Secondary GPT":
>>
>> https://en.wikipedia.org/wiki/GUID_Partition_Table
> 
> I know, in general, what GPT is and I am aware that there is a second
> backup copy of that partition table.  I am not aware of any specific
> "problems" this creates, in actual or common practice, relative to MBR.
> 
> I converted all of my own drives to GPT some time ago now, and I have
> never experienced any special issues or problems as a result of that
> change-over.  So I am still puzzled by your assertion that GPT can be
> in some way(s) more problematic that MBR.

If I use dd(1) to copy all of the blocks of a system disc with MBR 
partitioning to another device with a different (but sufficient) number 
of blocks. the target device will be laid out correctly, the partition, 
slice, and/or filesystem contents will be correct, and the disc work as 
a system disc.  I have done this countless times.


If I use dd(1) to copy all of the blocks of a system disc with GPT 
partitioning to another device with a different (but sufficient) number 
of blocks, the target device primary GPT table and partition, slice, 
and/or filesystem contents will be correct, but the secondary GPT table 
either will be in the wrong location (destination has more blocks) or 
will be missing (destination has fewer blocks).  My guess is that the 
disc would still work as a system disc (?), but I would need to fix the 
secondary GPT table.


David