[DEPRECATED] [GUID] GPT howto

graudeejs · #1 January 5th, 2009, 23:04

DEPRECATED: use gpart(8) instead

The next hot thing after 7.1R is GPT
old limit of 4 partitions is finally history
with GUID Partition table you can have up to 128 partitions.
Should i also say, that GPT will easily handle partitions over 2TB

MBR had problems with that

As soon as i heard [thanks to nsayers post]that it's possible to boot FreeBSD from GPT i had to test it

I have encountered some problems that i resolved on my own.
That's why i'm making this howto, so you don't have to spend few hours, just because something went wrong.

OK, here we go:
=================================
Preparing:

You'll need (or other media):
usb-flash
FreeBSD 7.1R DVD or FreeBSD-7.1R fixit cd

Backup data

During process we will delete all data on HDD, so
backup your valuable data and system, if you already have 7.1R on your PC

If you don't you need to upgrade your system to 7.1 [dunno if GPT works with 6.4]
before and after upgrading backup all data

I suggest you use GENERIC kernel, if you won't have right option, you can create system on GPT, but you can't boot it [another my fallback]

Copy necessary data
You need to make copy of /boot/pmbr and /boot/gptboot
because they are not on disks and this was my fallback nr1

You will need these files later.
I will copy them to my usb-flash

Once you have copied these files to some where, where you can get them, reboot in fixit mode [use cd]

Creating GUID partition tables

1) Erase MBR and write GPT table

Code:

$ gpt create -f ad0

You don't need to specify full path to device

2) Mount flash to /mnt

3) Create gpt boot partition

Code:

$ gpt boot -b /mnt/pmbr -g /mnt/gptboot ad0

by default this will create 64K partition, you can change this with -s and reduce to minimum (8K)
value behind argument -s must be size in sectors
1 sector is 512B
I suggest no changing it, who know if in 7.2 size might change
Also don't improvise to much, make sure boot partition is Nr 1 and root partition is Nr 2, otherwise you can't boot at all [another my fallback]

Note that when i say boot partition it doesn't mean /boot, it's different. /boot is in same partition as root

4) Create root partition (i'll make 256MB)

Code:

$ gpt add -t ufs -s 524288 ad0

5) To check what have you done

Code:

$ gpt show ad0

here's example output from one of my [already finished] test setup

Code:

fixit# gpt show ad0
      start        size  index     content
          0           1            PMBR
          1           1            Pri GPT header
          2          32            Pri GPT table
         34         128      1     GPT part - FreeBSD boot
        162     1048576      2     GPT part - FreeBSD UFS/UFS2
    1048738     2097152      3     GPT part - FreeBSD UFS/UFS2
    3145890     2097152      5     GPT part - FreeBSD UFS/UFS2
    5243042     1048576      6     GPT part - FreeBSD UFS/UFS2
   16777378     6291456      7     GPT part - FreeBSD UFS/UFS2
   23068834   168926701     11     GPT part - FreeBSD UFS/UFS2
  191995535    10485760     10     GPT part - FreeBSD UFS/UFS2
  202401295   109051904      9     GPT part - FreeBSD UFS/UFS2
  311533199     1048576      8     GPT part - FreeBSD swap
  312581775          32            Sec GPT table
  312581807           1            Sec GPT header

in this table might be mistakes [writing by hand sux], later i made better lay-out

Partitions that you already have created are accessible as
/dev/ad0p1 and /dev/ad0p2

6) Create more partitions /usr (5GB) and /var (512MB) and /tmp (512MB)

Code:

$ gpt add -t ufs -s 10485760 ad0
$ gpt add -t ufs -s 1048576 ad0
$ gpt add -t ufs -s 1048576 ad0

7) Create 512MB swap

Code:

$ gpt add -t swap -s 1048576 ad0

8) Create home partition with remaining free space

Code:

$ gpt add -t ufs ad0

9) Format partitions

Code:

$ newfs -nL root /dev/ad0p2
$ newfs -nUL usr /dev/ad0p3
$ newfs -nUL var /dev/ad0p4
$ newfs -nUL tmp /dev/ad0p5

I like labeling partitions, because i don't need to edit /etc/fstab each time something changes
It's also easier to track partitions if you got many of them

10) Mount root and run restore, then mount and restore usr, var and home.

After you're done, if you didn't use labels edit /etc/fstab
remember labels are placed in /dev/ufs/ directory

so for root it would look something like

Code:

/dev/ufs/root     /      ufs      rw    1 1

you need to edit your swap entry in fstab
when you create partition without using -i key, which is used to change partition NR, GPT will start with 1 and increment automatically.

so in this example swap will be /dev/ad0p5
and /home will be /dev/ad0p6

After you're done you can unmount partitions and reboot system.
It should boot with GENERIC.
If not, post here, I can resolve problems... like i did when i had to on my PC

Note also that you don't need to create bsdlabels anymore

TIP: it's also very easy to set up swap on most outer tracks of HDD

if you're interested in this look at -b parameter in manual

kernel options [make sure you have this in kernel config

Code:

options         GEOM_PART_GPT           # GUID Partition Tables.

For some reason, when i had all GEOM_PART_* in my kernel config i couldn't boot

common partition size cheat sheet
for megabytes:
sector count = 1024^2/512*MB_count
for gigabytes:
sector count = 1024^3/512*GB_count
==========
8KB = 16 sectors
32KB = 64 sect
64KB = 128 sect
256MB = 524288 sect
512MB = 1048576 sect

1GB = 2097152 sect
2GB = 4194304 sect
3GB = 6291456 sect
4GB = 8388608 sect
5GB = 10485760 sect
6GB = 12582912 sect
7GB = 14680064 sect
8GB = 16777216 sect
9GB = 18874368 sect

12GB = 25165824 sect
14GB = 29360128 sect
15GB = 31457280 sect
25GB = 52428800 sect

tip: 10GB can easily be calculated by adding 0 to 1GB sector count (this works for others as well )

If there's anything unclear please ask, i will answer and explain

resources:
gpt(8)

EDIT:
made few inaccuracy fixes

EDIT:
Important note
you you're adding gpt on top of geli and and used -s 4096 key, when you created geli, then
you will have to use these formulas:
for megabytes:
sector count = 1024^2/4096*MB_count
for gigabytes:
sector count = 1024^3/4096*GB_count

replace 4096 to value you have used

if you won't do that, you will get 32GB instead of 6GB partition

EDIT
if you want to do new install on gpt, create gpt partitions and fallow this guide:
http://daemonforums.org/showthread.php?t=1538

nsayer · #2 January 9th, 2009, 01:06

I would put your swap space adjacent to your boot partition. There are some very good reasons to do this:

1. By putting the swap near the beginning of the disk, it will boost its performance somewhat compared to it being at the end of the disk.

2. If you ever need to replace the boot partition (for example, if you move to an EFI machine, you'll need an EFI system partition instead), you'd simply delete the boot and swap partitions, make the new boot and then from the remaining space, make a swap partition.

graudeejs · #3 January 9th, 2009, 02:09

Beginning of the disk is in center, isn't it (inner track/cylinder)? [i'm not sure]

for data cd/dvd it is, so my guess would be it's also same for HDD
and if I'm right, and i hope I am, my swap is in outer track/cylinder of HDD

nsayer · #4 January 12th, 2009, 05:47

Seeks are the costly thing, regardless of whether block 0 is on the inside or outside of the disk. If you put the swap at the end of the disk, then you're setting up a situation where the machine is going to need to fiddle with lots of files from filesystems on the early blocks on the disk, and swap blocks in and out of swap space at the end of the disk. Lots of long seeks. Bad mojo.

trev · #5 January 16th, 2009, 11:46

Quote:

Copy necessary data
You need to make copy of /boot/pmbr and /boot/pmbr [1] because there [2] are not on disks and this was my fallback nr1

1. The same file?
2. "they" ?

graudeejs · #6 January 16th, 2009, 12:06

Quote:

Originally Posted by trev

1. The same file?
2. "they" ?

Thank you for noticing, I fixed my mistake [it was about 2 or 3 am when i wrote this

]

Code:

You need to make copy of /boot/pmbr and /boot/gptboot
because they are not on disks and this was my fallback nr1

trash · #7 October 13th, 2009, 00:44

anyone know how to fix corrupt gpt tables when migrating from solaris ?

graudeejs · #8 October 13th, 2009, 07:24

sorry, i dunno
but search forum, I remember there was 1 or 2 threads about this problem.

trash · #9 October 13th, 2009, 15:18

hi, thanks for the reply, yes ive also added my question to those threads, at least i think ive found all of them - almost asked the entire internet the question now

graudeejs · #10 December 5th, 2009, 23:05

To all looking at this howto....

yup, i saw you bluefish....
This is abit outdates. on FreeBSD 8 you need to use gpart for makeing gpt partitions... gpt is removed

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