Initializing a Linux Data Disk (fdisk)

Scenarios

This section uses CentOS 7.4 64bit to describe how to initialize a data disk attached to a server running Linux and use fdisk to partition the data disk.

The maximum partition size that MBR supports is 2 TiB and that GPT supports is 18 EiB. If the disk size you need to partition is greater than 2 TiB, partition the disk using GPT.

The fdisk partitioning tool is suitable only for MBR partitions, and the parted partitioning tool is suitable for both MBR and GPT partitions. For more information, see Scenarios and Disk Partitions.

The method for initializing a disk varies slightly depending on the OS running on the server. This document is used for reference only. For the detailed operations and differences, see the product documents of the corresponding OS.

Important

When using a disk for the first time, if you have not initialized it, including creating partitions and file systems, the additional space added to this disk in an expansion later may not be normally used.

Prerequisites

  • A data disk has been attached to a server and has not been initialized.

  • You have logged in to the server.

    • For how to log in to an ECS, see the Elastic Cloud Server User Guide.

    • For how to log in to a BMS, see the Bare Metal Server User Guide.

Creating and Mounting a Partition

The following example shows you how a new primary partition can be created on a new data disk that has been attached to a server. The primary partition will be created using fdisk, and MBR will be used. Furthermore, the partition will be formatted using the ext4 file system, mounted on /mnt/sdc, and configured to mount automatically at startup.

  1. Query what block devices are available on the server.

    fdisk -l

    Information similar to the following is displayed:

    [root@ecs-test-0001 ~]# fdisk -l
    
    Disk /dev/vda: 42.9 GiB, 42949672960 bytes, 83886080 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk label type: dos
    Disk identifier: 0x000bcb4e
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/vda1   *        2048    83886079    41942016   83  Linux
    
    Disk /dev/vdb: 107.4 GiB, 107374182400 bytes, 209715200 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    

    In the command output, this server contains two disks. /dev/vda and /dev/vdb. /dev/vda is the system disk, and /dev/vdb is the new data disk.

  2. Launch fdisk to partition the new data disk.

    fdisk New data disk

    In this example, run the following command:

    fdisk /dev/vdb

    Information similar to the following is displayed:

    [root@ecs-test-0001 ~]# fdisk /dev/vdb
    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.
    
    Device does not contain a recognized partition table
    Building a new DOS disklabel with disk identifier 0x38717fc1.
    
    Command (m for help):
    
  3. Enter n and press Enter to create a new partition.

    Information similar to the following is displayed:

    Command (m for help): n
    Partition type:
       p   primary (0 primary, 0 extended, 4 free)
       e   extended
    

    There are two types of disk partitions:

    • Choosing p creates a primary partition.

    • Choosing e creates an extended partition.

    Note

    If the MBR partition style is used, a maximum of 4 primary partitions, or 3 primary partitions and 1 extended partition can be created. The extended partition cannot be used directly and must be divided into logical partitions before use.

    Disk partitions created using GPT are not categorized.

  4. Enter p and press Enter to create a primary partition in this example.

    Information similar to the following is displayed:

    Select (default p): p
    Partition number (1-4, default 1):
    

    Partition number indicates the serial number of the primary partition. The value ranges from 1 to 4.

  5. Enter the serial number of the primary partition and press Enter. Primary partition number 1 is used in this example. One usually starts with partition number 1 when partitioning an empty disk.

    Information similar to the following is displayed:

    Partition number (1-4, default 1): 1
    First sector (2048-209715199, default 2048):
    

    First sector indicates the start sector. The value ranges from 2048 to 209715199, and the default value is 2048.

  6. Select the default start sector 2048 and press Enter.

    The system displays the start and end sectors of the partition's available space. You can customize the value within this range or use the default value. The start sector must be smaller than the partition's end sector.

    Information similar to the following is displayed:

    First sector (2048-209715199, default 2048):
    Using default value 2048
    Last sector, +sectors or +size{K,M,G} (2048-209715199, default 209715199):
    

    Last sector indicates the end sector. The value ranges from 2048 to 209715199, and the default value is 209715199.

  7. Select the default end sector 209715199 and press Enter.

    The system displays the start and end sectors of the partition's available space. You can customize the value within this range or use the default value. The start sector must be smaller than the partition's end sector.

    Information similar to the following is displayed:

    Last sector, +sectors or +size{K,M,G} (2048-209715199, default 209715199):
    Using default value 209715199
    Partition 1 of type Linux and of size 100 GiB is set
    
    Command (m for help):
    

    A primary partition has been created for the new data disk.

  8. Enter p and press Enter to print the partition details.

    Information similar to the following is displayed:

    Command (m for help): p
    
    Disk /dev/vdb: 107.4 GiB, 107374182400 bytes, 209715200 sectors
    Units = sectors of 1 * 512 = 512 bytes
    Sector size (logical/physical): 512 bytes / 512 bytes
    I/O size (minimum/optimal): 512 bytes / 512 bytes
    Disk label type: dos
    Disk identifier: 0x38717fc1
    
       Device Boot      Start         End      Blocks   Id  System
    /dev/vdb1            2048   209715199   104856576   83  Linux
    
    Command (m for help):
    

    Details about the /dev/vdb1 partition are displayed.

  9. Enter w and press Enter to write the changes to the partition table.

    Information similar to the following is displayed:

    Command (m for help): w
    The partition table has been altered!
    
    Calling ioctl() to re-read partition table.
    Syncing disks.
    

    The partition is created.

    Note

    In case that you want to discard the changes made before, you can exit fdisk by entering q.

  10. Synchronize the new partition table to the OS.

    partprobe

  11. Format the new partition with a desired file system format.

    mkfs -t File system format /dev/vdb1

    In this example, the ext4 format is used for the new partition.

    mkfs -t ext4 /dev/vdb1

    Information similar to the following is displayed:

    [root@ecs-test-0001 ~]# mkfs -t ext4 /dev/vdb1
    mke2fs 1.42.9 (28-Dec-2013)
    Filesystem label=
    OS type: Linux
    Block size=4096 (log=2)
    Fragment size=4096 (log=2)
    Stride=0 blocks, Stripe width=0 blocks
    6553600 inodes, 26214144 blocks
    1310707 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=2174746624
    800 block groups
    32768 blocks per group, 32768 fragments per group
    8192 inodes per group
    Superblock backups stored on blocks:
            32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
            4096000, 7962624, 11239424, 20480000, 23887872
    
    Allocating group tables: done
    Writing inode tables: done
    Creating journal (32768 blocks): done
    Writing superblocks and filesystem accounting information: done
    

    The formatting takes a period of time. Observe the system running status and do not exit.

    Important

    The partition sizes supported by file systems vary. Choose an appropriate file system format based on your service requirements.

  12. Create a mount point.

    mkdir Mount point

    In this example, the /mnt/sdc mount point is created.

    mkdir /mnt/sdc

    Note

    The /mnt directory exists on all Linux systems. If the mount point cannot be created, it may be that the /mnt directory has been accidentally deleted. You can run mkdir -p /mnt/sdc to create the mount point.

  13. Mount the new partition on the created mount point.

    mount Disk partition Mount point

    In this example, the /dev/vdb1 partition is mounted on /mnt/sdc.

    mount /dev/vdb1 /mnt/sdc

  14. Check the mount result.

    df -TH

    Information similar to the following is displayed:

    [root@ecs-test-0001 ~]# df -TH
    Filesystem     Type      Size  Used Avail Use% Mounted on
    /dev/vda1      ext4       43G  1.9G   39G   5% /
    devtmpfs       devtmpfs  2.0G     0  2.0G   0% /dev
    tmpfs          tmpfs     2.0G     0  2.0G   0% /dev/shm
    tmpfs          tmpfs     2.0G  9.1M  2.0G   1% /run
    tmpfs          tmpfs     2.0G     0  2.0G   0% /sys/fs/cgroup
    tmpfs          tmpfs     398M     0  398M   0% /run/user/0
    /dev/vdb1      ext4      106G   63M  101G   1% /mnt/sdc
    

    You should now see that partition /dev/vdb1 is mounted on /mnt/sdc.

    Note

    After the server is restarted, the disk will not be automatically mounted. To configure automount at startup, you will need to modify the /etc/fstab file. For details, see Configuring Automatic Mounting at System Start.

Configuring Automatic Mounting at System Start

The fstab file controls what disks are automatically mounted at startup. You can use fstab to configure your data disks to mount automatically. This operation will not affect the existing data.

The example here uses UUIDs to identify disks in the fstab file. You are advised not to use device names to identify disks in the file because device names are assigned dynamically and may change (for example, from /dev/vdb1 to /dev/vdb2) after a reboot. This can even prevent your disk from booting up.

Note

UUID is the unique character string for disk partitions in a Linux system.

  1. Query the partition UUID.

    blkid Disk partition

    In this example, the UUID of the /dev/vdb1 partition is queried.

    blkid /dev/vdb1

    Information similar to the following is displayed:

    [root@ecs-test-0001 ~]# blkid /dev/vdb1
    /dev/vdb1: UUID="0b3040e2-1367-4abb-841d-ddb0b92693df" TYPE="ext4"
    

    Carefully record the UUID, as you will need it for the following step.

  2. Open the fstab file using the vi editor.

    vi /etc/fstab

  3. Press i to enter editing mode.

  4. Move the cursor to the end of the file and press Enter. Then, add the following information:

    UUID=0b3040e2-1367-4abb-841d-ddb0b92693df /mnt/sdc                ext4    defaults        0 2
    
  5. Press Esc, enter :wq, and press Enter.

    The system saves the configurations and exits the vi editor.

  6. Verify that the disk is auto-mounted at startup.

    1. Unmount the partition.

      umount Disk partition

      In this example, run the following command:

      umount /dev/vdb1

    2. Reload all the content in the /etc/fstab file.

      mount -a

    3. Query the file system mounting information.

      mount | grep Mount point

      In this example, run the following command:

      mount | grep /mnt/sdc

      If information similar to the following is displayed, automatic mounting has been configured:

      root@ecs-test-0001 ~]# mount | grep /mnt/sdc
      /dev/vdb1 on /mnt/sdc type ext4 (rw,relatime,data=ordered)