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

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.

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