Re: GPT questions - gpt reliability, wedge naming, and filesystem scaling.

[Jeff Rizzo <riz%tastylime.net@localhost>]

On 6/19/14, 5:20 PM, Gerard Lally wrote:
> As an experiment I installed NetBSD 6 in a virtual machine to try and
> figure out GPT partitions and wedges. The experiment went well, and I
> learned for the first time how to install NetBSD by dropping to a shell
> from sysinst and running setup from the shell. As always Pierre-Philipp
> Braun was a great help.
>
> I have some questions. Answers to one or more of these questions are
> most welcome.
>
> 1) Is it safe to use GPT on NetBSD? The warnings on the gpt man page
> leave me less than 100% confident.

Yes, it's safe, provided you don't do something like try to have 
multiple partitioning schemes on a disk (which is hard to do by accident.)

> 2) As I understand it the NetBSD FFS filesystem is capable of growing
> to 8 zettabytes, but MBR partitioning combined with traditional
> disklabels meant we were restricted to 2 (or 4) TB partitions in
> practice. Am I right in saying that GPT and wedges remove this
> restriction, and we can now create partitions and filesystems greater
> than 4TB?
>
> 3) Using "NAME=dk0" in /etc/fstab didn't work for me; I had to specify
> /dev/dk0, /dev/dk1, etc.
> dk names also do not persist across reboots. For example, if I create a
> wedge as follows the dk_swap name reverts to dk1 after rebooting.
>
> dkctl wd0 addwedge dk_swap 64 2097152 swap
>
> This is not a big deal but it leaves me wondering how NAME=xxx in fstab
> is supposed to work. Does it work with GPT labels instead?

The NAME= stuff is in NetBSD-current but not -6, so it will first appear 
in NetBSD 7.0.
> 4) To get the sector offsets and sizes right I first created a
> traditional MBR + disklabel setup, sizing partitions in MB and taking
> note of the sector offsets and sector sizes this produced. I started at
> 2048. After destroying the MBR + disklabel setup I then used this
> information to create GPT partitions. I assume this is a safe way to do
> it? I am not really familiar with partition alignment, and even less so
> since the new disks came out.