gpart, bsdlabel and fdisk

Aristedes Maniatis ari at
Thu Oct 22 08:09:43 UTC 2009

On 22/10/09 6:01 PM, Scot Hetzel wrote:
> If anyone notices a problem with them, either let me know or update
> the wiki page.

That's very helpful, thanks Scot. It raises some questions:

* you don't have the instruction to perform "echo 'a 1' | fdisk -f - /dev/ad4" which Robert recommends

* Robert recommends GPT as the "easiest way to get ZFS on root working". Your instructions seem to lean more toward MBR "The advantage of using a MBR disk is that you can still dual boot with other Operating Systems.". Are there any downsides of using MBR which should be explained?

* I've seen posts here (sorry I don't have one handy) which recommend to not put swap on ZFS. Apart from crash dumps are there any other reasons to prefer one over the other? Your instructions explain both, without giving much of a guide about why you'd choose one. Is a 'native' swap faster than one on ZFS?

* you write LOADER_ZFS_SUPPORT=YES to src.conf, while previous instruction in this thread had it written to make.conf

* In order to follow will you need to run this from the live CD rather than the first install CD?

* At the top of the same page you give instructions for creating boot, swap and zfs partitions. But your instructions give block sizes very specific to your disks. It would be helpful to have something like:

   gpart add -b 34 -s 128 -t freebsd-boot ad0   (why 34? this is a different magic number to other magic numbers I've seen suggested)
   gpart add -b 162 -s 8G -t freebsd-swap ad0   (the 8G is more readable than specifying in sectors)

or even

   gpart add -b 162 -s 8G -t freebsd-swap -l swap-ad0 ad0  (the human readable label appears to be a nice feature of GPT)


   gpart show ad0
   and look for the offset and size following the "free" space.  [1]

   offset=`gpart show ad0 | grep '\- free \-' | awk '{print $1}'`
   size=`gpart show ad0 | grep '\- free \-' | awk '{print $2}'`

   gpart add -b $offset -s $size -t freebsd-zfs -l system-ad0 ad0

As a feature request it would be great if gpart supported "-s all" and made "-b" optional so that the next add starts at the beginning of the first free space.


[1] That's from Philipp Wuensche's instructions I found.

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