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Applies to: ✔️ Linux VMs
This article provides a solution to an issue where you fail to resize a Master Boot Record (MBR) partition for a data disk larger than 2 TB in an Azure Linux virtual machine.
Important
This article applies to supported endorsed Linux distributions.
Symptoms
When you run the fdisk command to resize an MBR partition, you receive the following warning message:
The size of this disk is 8.8 TB. DOS partition table format can't be used on drives for volumes larger than 2 TB for 512-byte sectors. Use parted(1) and GUID partition table format (GPT).
Here's a command sample:
sudo fdisk /dev/sdd
Here's a command output sample:
WARNING: The size of this disk is 8.8 TB (8796093022208 bytes).
DOS partition table format can not be used on drives for volumes
larger than (2199023255040 bytes) for 512-byte sectors. Use parted(1) and GUID
partition table format (GPT).
The device presents a logical sector size that is smaller than
the physical sector size. Aligning to a physical sector (or optimal
I/O) size boundary is recommended, or performance may be impacted.
Welcome to fdisk (util-linux 2.23.2).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help):
Command (m for help): d
Selected partition 1
Partition 1 is deleted
Command (m for help): n
Partition type:
p primary (0 primary, 0 extended, 4 free)
e extended
Select (default p): p
Partition number (1-4, default 1): 1
First sector (2048-4294967295, default 2048):
Using default value 2048
Last sector, +sectors or +size{K,M,G} (2048-4294967294, default 4294967294):
Using default value 4294967294
Partition 1 of type Linux and of size 2 TiB is set <--- HERE
Command (m for help): p
Disk /dev/sdd: 8796.1 GB, 8796093022208 bytes, 17179869184 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disk label type: dos
Disk identifier: 0x7024d1b6
Device Boot Start End Blocks Id System
/dev/sdd1 2048 4294967294 2147482623+ 83 Linux
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 16: Device or resource busy.
The kernel still uses the old table. The new table will be used at
the next reboot or after you run partprobe(8) or kpartx(8)
Syncing disks.
To verify the new size, follow these steps:
Inform the operating system (OS) of the partition table change by running the following command:
sudo partprobe /dev/sddCheck the new size of the partition
/dev/sdd1by running the following command:sudo lsblk -o NAME,TYPE,FSTYPE,LABEL,SIZE,RO,MOUNTPOINTThe command output shows the partition was resized only to 2 TB. Here's a command output example:
NAME TYPE FSTYPE LABEL SIZE RO MOUNTPOINT sda disk 32G 0 ├─sda1 part vfat 500M 0 /boot/efi ├─sda2 part xfs 500M 0 /boot ├─sda3 part xfs 31G 0 / └─sda4 part 2M 0 sdb disk 256G 0 └─sdb1 part ext4 256G 0 /mnt sdd disk 8T 0 └─sdd1 part ext4 2T 0 /appext4
Cause
The MBR, which contains the partition boundaries and partition (file system) type information, has an addressing limit of 2^32 sectors. The 32-bit address limitation within the MBR partition data structure limits the size of the disk and partition.
For 512-byte sectors, the address limitation for an MBR partition is 2 TB. For newer 4Kn devices, each logical sector is 2^32 x 4,096 bytes, or 16 TB.
Solution
Because the GUID Partition Table (GPT) has no sector address limitations, we recommend using GPT for a data disk of 2 TB or larger.
Here are two methods to use GPT on data disks:
Take a full backup of the data on the disk and re-create the GPT.
Change the partition type from MBR to GPT
Important
- Take a snapshot of the data disk before making any change.
- This change can only be done on a data disk, not an OS disk. If it's done on an OS disk, it will end up in a no boot situation.
- For Red Hat, it isn't possible to convert the MSDOS label to GPT without losing data.
Step 1: Identify the current partition table type
Use one of the following tools to check if the current data disk is MBR or GPT.
Step 2: Re-create the partition
Note
This section uses the gdisk tool to re-create the partition as an example.
Install the
gdisktool if it isn't installed in the Linux virtual machine:sudo yum install gdisk -yVerify the current size of the data disk：
sudo gdisk -l /dev/sdd | grep Disk | grep sectorsDisk /dev/sdd: 17179869184 sectors, 8.0 TiBStop the application running on the virtual machine and unmount the file system:
sudo systemctl stop myapp.service sudo umount /appext4Note
- Both
myapp.serviceand/appext4are example entries. Replace them accordingly. - If you need to increase the data disk size, you can do it now through your Azure account. A disk resizing in the Azure portal needs downtime. For more information, see Expand an Azure Managed Disk.
- Both
Re-create the partition number 1 by using the
gdiskcommand:sudo gdisk /dev/sddGPT fdisk (gdisk) version 0.8.10 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 dont want to convert your MBR partitions to GPT format! *************************************************************** Command (? for help): p --> PRINT PARTITION TABLE Disk /dev/sdd: 17179869184 sectors, 8.0 TiB Logical sector size: 512 bytes Disk identifier (GUID): 8A3DAD49-6916-4BC5-836B-2F90C5161C05 Partition table holds up to 128 entries First usable sector is 34, last usable sector is 17179869150 Partitions will be aligned on 2048-sector boundaries Total free space is 12884903870 sectors (6.0 TiB) Number Start (sector) End (sector) Size Code Name 1 2048 4294967294 2.0 TiB 8300 Linux filesystem Command (? for help): d --> DELETE PARTITION TABLE Using 1 Command (? for help): n --> CREATE NEW PARTITION TABLE Partition number (1-128, default 1): --> PARTITION 1 First sector (34-17179869150, default = 2048) or {+-}size{KMGTP}: 2048 --> SAME 1th SECTOR AS THE ORIGINAL PARTITION Last sector (2048-17179869150, default = 17179869150) or {+-}size{KMGTP}: --> HIT ENTER TO USE THE WHOLE SPACE, IN THIS CASE 8 TB Current type is 'Linux filesystem' Hex code or GUID (L to show codes, Enter = 8300): Changed type of partition to 'Linux filesystem' Command (? for help): p --> PRINT PARTITION TABLE Disk /dev/sdd: 17179869184 sectors, 8.0 TiB Logical sector size: 512 bytes Disk identifier (GUID): 8A3DAD49-6916-4BC5-836B-2F90C5161C05 Partition table holds up to 128 entries First usable sector is 34, last usable sector is 17179869150 Partitions will be aligned on 2048-sector boundaries Total free space is 2014 sectors (1007.0 KiB) Number Start (sector) End (sector) Size Code Name 1 2048 17179869150 8.0 TiB 8300 Linux filesystem Command (? for help): w --> APPLY CHANGES Final checks complete. About to write GPT data. THIS WILL OVERWRITE EXISTING PARTITIONS!! Do you want to proceed? (Y/N): Y --> "Y" TO APPLY OK; writing new GUID partition table (GPT) to /dev/sdd. Warning: The kernel is still using the old partition table. The new table will be used at the next reboot. The operation has completed successfully.Verify that the partition style is changed to GPT:
sudo gdisk -l /dev/sdd | grep -A4 '^Partition table scan:'Partition table scan: MBR: protective BSD: not present APM: not present GPT: presentCheck the size of the partition by running the following command:
sudo lsblk -o NAME,TYPE,FSTYPE,LABEL,SIZE,RO,MOUNTPOINTNAME TYPE FSTYPE LABEL SIZE RO MOUNTPOINT sda disk 32G 0 ├─sda1 part vfat 500M 0 /boot/efi ├─sda2 part xfs 500M 0 /boot ├─sda3 part xfs 31G 0 / └─sda4 part 2M 0 sdb disk 256G 0 └─sdb1 part ext4 256G 0 /mnt sdd disk 8T 0 └─sdd1 part ext4 2T 0 /appext4Unmount the file system that was mounted automatically and repair it:
sudo umount /appext4 sudo fsck.ext4 -fy /dev/sdd1e2fsck 1.42.9 (28-Dec-2013) 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/sdd1: 6728/134217728 files (0.2% non-contiguous), 8849024/536870655 blocksRemount the file system:
sudo mount /appext4Resize the file system:
If the file system is
ext4, run the following command:sudo resize2fs /dev/sdd1resize2fs 1.42.9 (28-Dec-2013) Filesystem at /dev/sdd1 is mounted on /appext4; on-line resizing required old_desc_blocks = 256, new_desc_blocks = 1024 The filesystem on /dev/sdd1 is now 2147483387 blocks long.If the file system is
XFS, run the following command:sudo xfsgrowfs /dev/sdd1Verify the new size:
sudo lsblk -o NAME,TYPE,FSTYPE,LABEL,SIZE,RO,MOUNTPOINTNAME TYPE FSTYPE LABEL SIZE RO MOUNTPOINT sda disk 32G 0 ├─sda1 part vfat 500M 0 /boot/efi ├─sda2 part xfs 500M 0 /boot ├─sda3 part xfs 31G 0 / └─sda4 part 2M 0 sdb disk 256G 0 └─sdb1 part ext4 256G 0 /mnt sdc disk 1T 0 └─sdc1 part LVM2_member 1T 0 └─vgtest1-lvol1 lvm ext4 500G 0 sdd disk 8T 0 └─sdd1 part ext4 8T 0 /appext4 sde disk 1T 0
Third-party information disclaimer
The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.
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