How do I convert my EC2 CentOS instance's default MBR partitioning scheme to GPT in order to bypass the 2 TiB limit for MBR partitions on my EBS volume?

Last updated: 2020-09-02

My Amazon Elastic Compute Cloud (Amazon EC2) instance is running CentOS 7 from the AWS Marketplace by centos.org. How can I convert the default MBR partitioning scheme on my Amazon Elastic Block Store (Amazon EBS) volume to the GPT partitioning scheme to bypass the 2 TiB limit for MBR partitions?

Resolution

Warning: Before stopping and starting your instance, be sure you understand the following:

  • Instance store data is lost when you stop and start an instance. If your instance is instance store-backed or has instance store volumes containing data, the data is lost when you stop the instance. For more information, see Determining the root device type of your instance.
  • If your instance is part of an Amazon EC2 Auto Scaling group, stopping the instance may terminate the instance. If you launched the instance with Amazon EMR, AWS CloudFormation, or AWS Elastic Beanstalk, your instance might be part of an AWS Auto Scaling group. Instance termination in this scenario depends on the instance scale-in protection settings for your Auto Scaling group. If your instance is part of an Auto Scaling group, then temporarily remove the instance from the Auto Scaling group before starting the resolution steps.
  • Stopping and starting the instance changes the public IP address of your instance. It's a best practice to use an Elastic IP address instead of a public IP address when routing external traffic to your instance. If you are using Route 53, you might have to update the Route 53 DNS records when the public IP changes.

Note: It's a best practice to create a backup of your EBS volume before beginning any resolution steps.

1.    Open the Amazon EC2 console.

2.    Launch an instance from an AWS Marketplace Amazon Machine Image (AMI) running CentOS 7.

3.    Launch a second instance in the same Availability Zone as the first instance and from the same CentOS AMI with a 3TiB root volume.

Note: If you already have a CentOS 7 instance, you don't need to launch a new CentOS 7 instance. For CentOS 7, modify the root volume in order to extend its size to over 2 TiB.

4.    Stop the instance with the 3 TiB root volume and stop the instance you created in step 2.

Note: CentOS 7 is from an AWS Marketplace AMI, so you need to stop your instance before attaching a volume with AWS Marketplace codes. If you don't stop the instance, the following error occurs:

"Error attaching volume: Cannot attach volume 'vol-xxxxxxxxxxxxxxxxx' with Marketplace codes as the instance 'i-xxxxxxxxxxxxxxxx' is not in the 'stopped' state."

5.    Detach the root volume (/dev/xvda or /dev/sda1) from the stopped instance and then attach it to the instance you created in step 2 as /dev/sdf.

Note: Use the Xen platform instance type, such as t2. If you use the Nitro platform, such as t3, the device name changes to nvmeXn1.

6.    Start the instance you launched in step 2 and connect to it using SSH.

7.    Use the lsblk command to view the root partition of /dev/sdf. The root partition of /dev/sdf is only 2 TiB, as shown in the following example:

# lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
(snip)
xvdf    202:80    0   3T  0 disk 
└─xvdf1 202:81    0   2T  0 part 
(snip)

Note: /dev/xvdf1 might mount as the root file system "/". If this occurs, stop and start the instance a few times until /dev/xvda1 mounts as the root file system.

# 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   3T  0 disk 
└─xvdf1 202:81   0   2T  0 part 

8.    Use the gdisk tool to convert the partition table from MBR to GPT.

Note: If the gdisk tool isn't already installed, you can install it using the command sudo yum install gdisk -y.

# sudo gdisk /dev/xvdf
GPT fdisk (gdisk) version 1.0.1
Partition table scan:
  MBR: MBR only
  BSD: not present
  APM: not present
  GPT: not present

***************************************************************
Found invalid GPT and valid MBR; converting MBR to GPT format
in memory. THIS OPERATION IS POTENTIALLY DESTRUCTIVE! Exit by
typing 'q' if you don't want to convert your MBR partitions
to GPT format!

9.    Enter the following commands at the prompts to create a GPT partition. Type enter at the Last sector prompt to use the default sector number 2047.

Command (? for help): n                                                                                                        
Partition number (2-128, default 2): 128                                                                               
First sector (34-6291455966, default = 4294967296) or {+-}size{KMGTP}: 34                     
Last sector (34-2047, default = 2047) or {+-}size{KMGTP}:                                                  
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300): ef02                                                     
Changed type of partition to 'BIOS boot partition'

Note: In the preceding example, ef02 is the BIOS boot partition number.

10.    Enter the following commands at the prompts to delete the root partition:

Command (? for help): d                                                                                                         
Partition number (1-128): 1

11.    Enter the following commands at the prompts to recreate the root partition to 3 TB. In the First sector, Last sector, and Hex code or GUID prompts, type enter to use the default settings.

Command (? for help): n                                                                                                         
Partition number (1-128, default 1): 1                                                                                     
First sector (2048-6291455966, default = 2048) or {+-}size{KMGTP}:                                  
Last sector (2048-6291455966, default = 6291455966) or {+-}size{KMGTP}:                       
Current type is 'Linux filesystem'
Hex code or GUID (L to show codes, Enter = 8300):                                                             
Changed type of partition to 'Linux filesystem'

12.    Enter the following commands at the prompts to save the GPT partition table:

Command (? for help): w                                                                                                        
Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING
PARTITIONS!!
Do you want to proceed? (Y/N): y                                                                                          
OK; writing new GUID partition table (GPT) to /dev/xvdf.
The operation has completed successfully.

Run the gdisk command to view the new partition information:

$ sudo gdisk -l /dev/xvdf
GPT fdisk (gdisk) version 0.8.10

Partition table scan:
  MBR: protective
  BSD: not present
  APM: not present
  GPT: present

Found valid GPT with protective MBR; using GPT.
Disk /dev/xvda: 6291456000 sectors, 2.9 TiB
Logical sector size: 512 bytes
Disk identifier (GUID): 35D6B819-1C79-4EC0-920F-4D1191609505
Partition table holds up to 128 entries
First usable sector is 34, last usable sector is 6291455966
Partitions will be aligned on 8-sector boundaries
Total free space is 0 sectors (0 bytes)

Number  Start (sector)    End (sector)  Size       Code  Name
   1            2048      6291455966   2.9 TiB     8300  Linux filesystem
 128              34            2047   1007.0 KiB  EF02  BIOS boot partition

13.    Use the file system check and repair tool to check that the file system of device /dev/xvdf1 is correct.

CentOS 7:

# sudo xfs_repair /dev/xvdf1
Phase 1 - find and verify superblock...
        - reporting progress in intervals of 15 minutes
Phase 2 - using internal log
        - zero log...
        - scan filesystem freespace and inode maps...
        - 05:27:07: scanning filesystem freespace - 1025 of 1025 allocation groups done
        - found root inode chunk
Phase 3 - for each AG...
        - scan and clear agi unlinked lists...
        - 05:27:07: scanning agi unlinked lists - 1025 of 1025 allocation groups done
        - process known inodes and perform inode discovery...
        - agno = 960
        - agno = 0
        - agno = 240
        - agno = 480

(snip)
        - agno = 238
        - agno = 239
        - 05:27:08: process known inodes and inode discovery - 25856 of 25856 inodes done
        - process newly discovered inodes...
        - 05:27:08: process newly discovered inodes - 1025 of 1025 allocation groups done
Phase 4 - check for duplicate blocks...
        - setting up duplicate extent list...
        - 05:27:08: setting up duplicate extent list - 1025 of 1025 allocation groups done
        - check for inodes claiming duplicate blocks...
        - agno = 0
        - agno = 1
        - agno = 2
        - agno = 3
        - agno = 4

(snip)
        - agno = 1021
        - agno = 1022
        - agno = 1023
        - agno = 1024
        - 05:27:08: check for inodes claiming duplicate blocks - 25856 of 25856 inodes done
Phase 5 - rebuild AG headers and trees...
        - 05:27:08: rebuild AG headers and trees - 1025 of 1025 allocation groups done
        - reset superblock...
Phase 6 - check inode connectivity...
        - resetting contents of realtime bitmap and summary inodes
        - traversing filesystem ...
        - traversal finished ...
        - moving disconnected inodes to lost+found ...
Phase 7 - verify and correct link counts...
        - 05:27:08: verify and correct link counts - 1025 of 1025 allocation groups done
done

CentOS 6:

# sudo e2fsck -f /dev/xvdf1
e2fsck 1.41.12 (17-May-2010)
Pass 1: Checking inodes, blocks, and sizes
Pass 2: Checking directory structure
Pass 3: Checking directory connectivity
Pass 4: Checking reference counts
Pass 5: Checking group summary information
/dev/xvdf1: 18734/524288 files (0.2% non-contiguous), 284948/2096896 blocks

14.    Run the xfs_growfs or resize2fs command to resize the file system in order to extend it to 3 TB.

Note: It might take between few minutes to resize the file system.

CentOS 7:

# sudo mount -o nouuid /dev/xvdf1 /mnt

# sudo xfs_growfs /dev/xvdf1
meta-data=/dev/xvdf1             isize=512    agcount=1025, agsize=524224 blks
         =                       sectsz=512   attr=2, projid32bit=1
         =                       crc=1        finobt=0 spinodes=0
data     =                       bsize=4096   blocks=536870656, imaxpct=25
         =                       sunit=0      swidth=0 blks
naming   =version 2              bsize=4096   ascii-ci=0 ftype=1
log      =internal               bsize=4096   blocks=2560, version=2
         =                       sectsz=512   sunit=0 blks, lazy-count=1
realtime =none                   extsz=4096   blocks=0, rtextents=0
data blocks changed from 536870656 to 786431739

CentOS 6:

# sudo resize2fs /dev/xvdf1
resize2fs 1.41.12 (17-May-2010)
Resizing the filesystem on /dev/xvdf1 to 786431739 (4k) blocks.

The filesystem on /dev/xvdf1 is now 786431739 blocks long.

15.    Install Grub on the device /dev/xvdf1 and configure it using the following commands.

Note: Grub installation isn't required for S 6. If you're using CentOS 6, skip to step 16.

CentOS 7:

sudo mount --bind /proc /mnt/proc
sudo mount --bind /sys /mnt/sys
sudo mount --bind /dev /mnt/dev
sudo chroot /mnt /bin/bash
grub2-install /dev/xvdf
exit
sudo umount -l /mnt/dev
sudo umount -l /mnt/sys
sudo umount -l /mnt/proc
sudo umount -l /mnt

16.    Stop the instance.

17.    Detach the volume /dev/xvdf from the stopped instance.

18.    Attach the volume /dev/xvdf back to its original instance as /dev/sda1.

19.    Start the original instance and connect to it with SSH.

20.    Run the lsblk command to verify that the root volume on your original instance now has 3 TiB of space.

$ lsblk
NAME    MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
xvda    202:0    0   3T  0 disk 
└─xvda1 202:1    0   3T  0 part /