On 2016-03-18 17:41, Freddie Cash wrote:

On Fri, Mar 18, 2016 at 10:39 AM, Conrad Meyer <c...@freebsd.org
<mailto:c...@freebsd.org>> wrote:

    On Fri, Mar 18, 2016 at 10:03 AM, Allan Jude <allanj...@freebsd.org
    <mailto:allanj...@freebsd.org>> wrote:
     > On 2016-03-18 12:33, Guido Falsi wrote:
     >> Hi,
     >> I have just update one of my machines and noticed the booloaders
     >> got quite fat in the last few days, some by a big margin.
     >> on an updated machine(r296993):
     >> -r--r--r--  1 root  wheel   85794 Mar 18 16:47 /boot/gptboot
     >> from a machine I still have not updated(r296719):
     >> -r--r--r--  1 root  wheel   16059 Mar 13 21:01 /boot/gptboot

    So the loader grew 70 kB.  How big are your disks?

     >> I noticed because mu gpt boot partition is 64K and gptzfsboot just
     >> passed 100K.
     > This is a side effect of the loader gaining the ability to boot
    from GELI
     > encrypted partitions.
     > ...
     > Maybe we should be putting the GELI enabled boot blocks in a
     > filename? I generally wanted to avoid creating a new version of each
     > bootcode with GELI support.

    I think we should just suggest that boot partitions be much larger
    than 64kB (1MB is still <0.1% of any disk sold today) and not worry
    about it too much.  Embedded applications can disable GELI loader
    support to save a few bytes.

​The boot partition doesn't necessarily need ​
​to be 1 MB (and can't due to some issues with the assembler used right
now, or something like that).  We just need to make sure people have
slack space in their partition table to expand into in the future.

Using "-a 1M" in your gpart command to create your first data partition
gives you that slack space.

gpart create -s gpt ada0
gpart add -t freebsd-boot -s 256K -l boot ada0
gpart add -t freebsd-ufs  -s 10G  -l root -a 1M ada0

That leaves ~756 KB of free space between the end of the boot partition
and the start of the first data partition.  Increasing the size of the
boot partition in the future is as easy as (no formatting of disks

gpart delete -i 1 ada0
gpart add -t freebsd-boot -s 512K -l boot ada0
gpart bootcode -b ... -p ... ada0

It's a handy pattern I've gotten used to over the years, ever since the
first 4K sector harddrives were advertised (as alignment of filesystems
was/is *very* important)​.

Even on disks that will be used solely for ZFS I've taken to creating
GPT partitions starting at 1 MB.  And it's saved me from having to
reformat disks when moving from a separate root filesystem (no USB
sticks) to root-on-ZFS as there was 1 MB of free space at the start of
every disk for creating boot partitions.  :)

Freddie Cash
fjwc...@gmail.com <mailto:fjwc...@gmail.com>

This also has the handy side effect of allowing you to switch to booting with UEFI, which currently uses an 800kb fat file system

Allan Jude
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