upgrade stable/12 -> stable/13 zfs + boot partition Mediasize 64K

[Russell L. Carter]

On 2/11/21 5:43 PM, Freddie Cash wrote:
> Sorry, meant 256 KB or 512 KB, not MB!
> 
> On Thu, Feb 11, 2021 at 4:43 PM Freddie Cash <fjwcash at gmail.com> wrote:
> 
>> On Thu, Feb 11, 2021 at 4:35 PM Russell L. Carter <rcarter at pinyon.org>
>> wrote:
>>
>>> Greetings,
>>>
>>> I really want to jump from stable/12 to stable/13 but one thing is
>>> causing a hesitancy.  And that is, my main raidz2 system has
>>> a system boot zfs mirror pair that has boot partition size
>>> (Mediasize) of 64K, and when I tried to zpool upgrade that pool a
>>> year or 2 ago I got some scary message something like "boot
>>> partition size is not large enough".  I asked about this on the
>>> lists but never received an answer.  So, laziness required me
>>> to ignore the problem and not zpool upgrade any of my 15 or so
>>> zpools in the interim.
>>>
>>> A few weeks ago I tried to make buildworld/installworld upgrade
>>> 12->13 but the boot failed in the mounting filesystems phase with it
>>> couldn't find a bootable target.  So after restoring 12 I decided
>>> to wait a bit.  In the interim I have upgraded every zpool but that
>>> one system pool.  All the other freebsd-boot partitions have a size
>>> of 512K.
>>>
>>> So what is the current advice?  Is a freebsd-boot partition size
>>> of 64K laughably obsolete, and I should get with the program and
>>> repartition those disks, or can I march blindly into the upgrade?
>>>
>>> I guess I just want to understand where these sizes are going in
>>> the future.
>>>
>>> That is laughably small and you need to enter the 21st century.  ;)
>>
>> I believe the recommendation is 256 MB or even 512 MB these days.
>>
>> If you partitioned your disks using "-a 1M" with gpart(8) for the
>> freebsd-zfs partition, then you'll have some slack space between it and the
>> freebsd-boot partition. Just delete the freebsd-boot partition and create a
>> larger one in it's place.  I did something similar with some drives that
>> were part of a separate storage pool that I wanted to make bootable, by
>> creating a freebsd-boot partition in the slack space before the freebsd-zfs
>> partition.
>>
>> If you don't have that slack space at the front, you will need to detach
>> one of the drives from the mirror, re-partition it, then attach it back to
>> the mirror.  Rinse and repeat for the other side.  ZFS shouldn't notice the
>> pool is smaller by 1 MB (there's some internal slack space to allow you to
>> add drives that are labelled as the same size, but actually have different
>> numbers of sectors).
>>
>> Cheers,
>> Freddie
>>
> 
> 

That's what I wanted to know, thanks a lot.  I need to practice
replacing drives on that mirror anyway.  Although I will study
carefully the partition boundaries to see if your shortcut might
work.

I'm a FreeBSD person until I die so I should to get these lower level
details nailed.

Best!
Russell