ZFS and GPT boot - size issue bootblock v.s. default of sysinstall

[Dirk-Willem van Gulik]

On a default ZFS install (late 2014, 10.x) of a few years hence it seems sysinstall selected 64k as the default size of partition 1: with the bootblock:

sudo gpart show
=>        34  7814037101  ada0  GPT  (3.6T)
          34           6        - free -  (3.0K)
          40         128     1  freebsd-boot  (64K)
         168    67108864     2  freebsd-swap  (32G)
    67109032  7746928096     3  freebsd-zfs  (3.6T)
  7814037128           7        - free -  (3.5K)

…. lots of disks snipped …..

=>        34  7814037101  ada35  GPT  (3.6T)
          34           6        - free -  (3.0K)
          40         128     1  freebsd-boot  (64K)
         168    67108864     2  freebsd-swap  (32G)
    67109032  7746928096     3  freebsd-zfs  (3.6T)
  7814037128           7        - free -  (3.5K)

Fair to assume that this (the 64k) is the reason that from 11.x onwards; 

	gpart bootcode -b /boot/pmbr -p /boot/gptzfsboot -i 1 ada0 

fails with an immediate:

	gpart: /dev/ada1p1: not enough space 

as gptzfsboot has grown in recent years to something towards the 90k mark ?

	-r--r--r-- 1 root wheel 88898 Dec 24 11:52 /boot/gptzfsboot
	
And I guess avoiding a rebuild would mean something like gently disabling swap; shifting partition 1 & 2 carefully an so on ? Or is there a more clever way? ZFS has *already* been upgraded.

 Or am I missing something ?

Thanks,

Dw