Ever wondered how to convert your old MBR based instances to new GPT ones? This will help you to have larger boot volumes and lots of other benefits.
This is the step by step procedure that you can follow, but please note this is not copy and past procedure so you should make sure that the device names, units and other variables are suitable for your environment. When you convert the partition table, you should create new AMI that will have GPT by default so you don't have to repeat the procedure for each instance.
1) For test you can launch two instances (eg: UBUNTU and TEMP). The TEMP instance will be used to attach the root volume from the UBUNTU (original) instance.
Please don't use the same Ubuntu 10.06 AMI (to avoid complications later with attaching two root volumes with the same UUID). You can use Ubuntu 10.04 for TEST and you own AMI for UBUNTU instance.
When the instances are fully launched, stop both instances and detach/attach the root volume from UBUNTU instances to TEMP as /dev/sdf (secondary volume).
Now start the UBUNTU instance, ssh to it and check if the disk are present using "lsblk" tool.
ubuntu@ip-172-31-45-175:~$ sudo su -
root@ip-172-31-45-175:~# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda 202:0 0 8G 0 disk
└─xvda1 202:1 0 8G 0 part /
xvdf 202:80 0 3.9T 0 disk
└─xvdf1 202:81 0 2T 0 part
We can see that we have the secondary 4TiB disk (/dev/xvdf) present and that is what we expected.
In order to convert /dev/xvdf from MBR to GPT you have to create new partition table with "parted" or other GPT aware tools. I will use parted in this example and it should be installed on Ubuntu by default.
Note that you will have to create another partition bios_grub that is necessary for GPT partitions and this partition will hold the rest of the grub boot data (basically GRUB stabe 1.5) that can't fit into stage 1.
Enter parted using "parted /dev/xvdf" command and type "print" to check the current partition table. You will notice that the type is "Partition Table: msdos" and we need to change this.
$ sudo parted /dev/xvdf
(parted) unit s
(parted) print
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvdf: 8388608000s
Sector size (logical/physical): 512B/512B
Partition Table: msdos
Number Start End Size Type File system Flags
1 16065s 4294967294s 4294951230s primary ext4 boot
Please write down the "Start" sector numbers for the existing partition. We will need this to recreate the GPT partition later.
First step is to create new GPT partition table using "mklabel" command.
(parted) mklabel
New disk label type? Gpt
Warning: The existing disk label on /dev/xvdf will be destroyed and all data on this disk will be lost. Do you want to continue?
Yes/No? Yes
(parted) print
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvdf: 8388608000s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number Start End Size File system Name Flags
Now we should recreate the root partition using the "Start" sector value we wrote in the previous step. This time we will use the 100% of the free space and this way the partition will be 4 TiB in size on next boot.
(parted) mkpart
Partition name? []?
File system type? [ext2]? ext4
Start? 16065s
End? 100%
Warning: The resulting partition is not properly aligned for best performance.
Ignore/Cancel? Ignore
(parted) print
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvdf: 8388608000s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number Start End Size File system Name Flags
1 16065s 8388607966s 8388591902s ext4
(parted) quit
Information: You may need to update /etc/fstab.
At this moment we have the root partition recreated but we are still missing bios_grub partition that is necessary for GRUB to work on GPT partition scheme.
(parted) unit s
(parted) mkpart
Partition name? []?
File system type? [ext2]?
Start? 2048
End? 6144
(parted) print
Model: Xen Virtual Block Device (xvd)
Disk /dev/xvdf: 8388608000s
Sector size (logical/physical): 512B/512B
Partition Table: gpt
Number Start End Size File system Name Flags
2 2048s 6144s 4097s
1 16065s 8388607966s 8388591902s ext4
(parted) quit
Information: You may need to update /etc/fstab.
At this point we have both partition created and ready to proceed.
The next step is to set the proper partition type using "parted set" command. After that we will install grub bootloader since it's not present anymore since we recreated the partition scheme.
$ sudo parted /dev/xvdf set 2 bios_grub on
Information: You may need to update /etc/fstab.
In order to install grub we will need to mount (temporarily) the root volume to /mnt mount point.
$ sudo mount /dev/xvdf1 /mnt/
$ sudo grub-install --boot-directory=/mnt/boot /dev/xvdf
$ sudo umount /mnt
At this point (if you don't have any errors) the process should be completed.
Next step would be to stop the instance, detach the secondary volume and attach it back to the UBUNTU instance as /dev/sda1 (root volume).
The new instance should start with the root volume of 4TiB.
