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

On Fri, Jun 20, 2014 at 01:20:03AM +0100, Gerard Lally wrote:
> 1) Is it safe to use GPT on NetBSD? The warnings on the gpt man page
> leave me less than 100% confident.

Yes.  I am using GPT on my laptop in a multiboot netbsd/linux/win8 set
up.  It takes some care to set up but works fine.  I do intend to write
up what I have done when I have some time.

> 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?

Odd, mine persist:

# dkctl /dev/rwd0d listwedges
/dev/rwd0d: 12 wedges:
dk0: Basic data partition, 1572864 blocks at 2048, type: 
dk1: 1176b336-7aba-4a02-82ea-2493e09215e3, 1572864 blocks at 1574912, type: 
dk2: EFI system partition, 532480 blocks at 3147776, type: msdos
dk3: Microsoft reserved partition, 262144 blocks at 3680256, type: 
dk4: ed1a0b68-7012-4994-b58e-34710d9e5244, 102400000 blocks at 3942400, type: 
dk5: 0e02bd01-2798-47c9-bd3e-1776faafdf4f, 102400000 blocks at 106342400, type: 
dk7: NetBSD-root, 122880000 blocks at 208742400, type: ffs
dk8: NetBSD-swap, 24576000 blocks at 331622400, type: swap
dk9: NetBSD-home, 364544000 blocks at 356198400, type: cgd

I am using a sort of recent -current though, perhaps that is the

> 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.

If you just stick to multiples of 4k you are probably ok, the concepts
of cylinders and heads became meaningless quite some time ago so just
treat the disk as a blob of sectors

Brett Lymn
Staple Guns: because duct tape doesn't make that KerCHUNK sound -

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