Solved gpart add -b 2048 starts partition at LBA 2079 (???)

[rowan194]

[SOLUTION]
Realised I was doing this on a machine with quite an old install (FreeBSD 10)
When tried on a machine with a more modern version it works as expected. I guess it's a bug that was fixed.
I'll leave the text here in case someone else happens to come across the same issue.

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I'm trying to extend the last partition on a MicroSD card. There's already data on the card, so it's vital that partition offsets remain exactly the same.

I want the first partition to start at LBA 2048, but for some reason gpart places it at LBA 2079.

Original layout before any changes:

# gpart show da0
=>       63  124735425  da0  MBR  (59G)
         63       1985       - free -  (993K)
       2048     262144    1  !12  (128M)
     264192   30851073    2  linux-data  (15G)
   31115265   93620223       - free -  (45G)

And here's the config used by gpart backup, with the size of the last partition enlarged:

# gpart backup da0 > config.txt
<edit config.txt>
# cat config.txt
MBR 4
1        !12      2048    262144
2 linux-data    264192 123731968

But when I do cat config.txt | gpart restore -F da0, gpart sets the first partition to start at LBA 2079 instead of LBA 2048:

# cat config.txt | gpart restore -F da0
# gpart show da0
=>       63  124735425  da0  MBR  (59G)
         63       2016       - free -  (1.0M)
       2079     262080    1  !12  (128M)
     264159         63       - free -  (32K)
     264222  123731937    2  linux-data  (59G)
  123996159     739329       - free -  (361M)

I also tried deleting the partitions, and manually creating the first, with the same result:

# gpart delete -i 2 da0
# gpart delete -i 1 da0
# gpart add -t \!12 -i 1 -b 2048 -s 262144 da0
# gpart show da0
=>       63  124735425  da0  MBR  (59G)
         63       2016       - free -  (1.0M)
       2079     262080    1  !12  (128M)
     264159  124471329       - free -  (59G)

I also tried adding "-a 512b" and "-a 1" in case it was trying to align to something larger than a sector, but that does not change the behaviour.

Why does gpart ignore my explicit request to start at LBA 2048?