# Initializing a Linux Data Disk (parted)

#### Scenarios

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

The maximum disk capacity supported by MBR is 2 TB, and that supported by GPT is 18 EB. Therefore, use the GPT partition style if your disk capacity is larger than 2 TB. In Linux, if you choose to use the GPT partition style, the fdisk partitioning tool cannot be used. Use the parted partitioning tool instead. For details about disk partition styles, see Scenarios and Disk Partitions.

The method for initializing a disk varies 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.

#### 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 partition can be created on a new data disk that has been attached to a server. The partition will be created using parted, and GPT is used as the partition style. Furthermore, the partition will be formatted using the ext4 file system, mounted on /mnt/sdc, and configured automatic mounting at system start.

1. Run the following command to query information about the new data disk:

   lsblk

   Information similar to the following is displayed:

       root@ecs-test-0001 ~]# lsblk
       NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
       vda    253:0    0   40G  0 disk
       └─vda1 253:1    0   40G  0 part /
       vdb    253:16   0  100G  0 disk

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

2. Run the following command to enter parted to partition the new data disk:

   parted New data disk

   In this example, run the following command:

   parted /dev/vdb

   Information similar to the following is displayed:

       [root@ecs-test-0001 ~]# parted /dev/vdb
       GNU Parted 3.1
       Using /dev/vdb
       Welcome to GNU Parted! Type 'help' to view a list of commands.
       (parted)

3. Enter p and press Enter to view the current disk partition style.

   Information similar to the following is displayed:

       (parted) p
       Error: /dev/vdb: unrecognised disk label
       Model: Virtio Block Device (virtblk)
       Disk /dev/vdb: 107GB
       Sector size (logical/physical): 512B/512B
       Partition Table: unknown
       Disk Flags:
       (parted)

   In the command output, the Partition Table value is unknown, indicating that no partition style is set for the new disk.

4. Run the following command to set the disk partition style:

   mklabel Disk partition style

   In this example, run the following command to set the partition style to GPT: (Disk partition styles can be MBR or GPT.)

   mklabel gpt

   The maximum disk capacity supported by MBR is 2 TB, and that supported by GPT is 18 EB. Because a data disk currently supports up to 32 TB, use the GPT partition style if your disk capacity is larger than 2 TB.

   If you change the disk partition style after the disk has been used, the data on the disk will be cleared. Therefore, select a proper disk partition style when initializing the disk.

5. Enter p and press Enter to view the disk partition style.

   Information similar to the following is displayed:

       (parted) mklabel gpt
       (parted) p
       Model: Virtio Block Device (virtblk)
       Disk /dev/vdb: 107GB
       Sector size (logical/physical): 512B/512B
       Partition Table: gpt
       Disk Flags:

       Number  Start  End  Size  File system  Name  Flags

       (parted)

   In the command output, the Partition Table value is gpt, indicating that the disk partition style is GPT.

6. Enter unit s and press Enter to set the measurement unit of the disk to sector.
7. Run the following command and press Enter:

   mkpart Partition name Start sector End sector

   In this example, run the following command:

   mkpart test 2048s 100%

   In this example, one partition is created for the new data disk. Variable 2048s indicates the disk start sector, and variable 100% indicates the disk end sector. The two values are used for reference only. You can determine the number of partitions and the partition size based on your service requirements.

   Information similar to the following is displayed:

       (parted) mkpart opt 2048s 100%
       (parted)

8. Enter p and press Enter to view details about the new partition.

   Information similar to the following is displayed:

       (parted) p
       Model: Virtio Block Device (virtblk)
       Disk /dev/vdb: 209715200s
       Sector size (logical/physical): 512B/512B
       Partition Table: gpt
       Disk Flags:

       Number  Start  End         Size        File system  Name  Flags
        1      2048s  209713151s  209711104s               test

       (parted)

9. Enter q and press Enter to exit parted.

   Information similar to the following is displayed:

       (parted) q
       Information: You may need to update /etc/fstab.

   You can set automatic disk mounting by updating the /etc/fstab file. Before updating the file, set the file system format for the partition and mount the partition on the mount point.

10. Run the following command to view the disk partition information:

    lsblk

    Information similar to the following is displayed:

        [root@ecs-test-0001 ~]# lsblk
        NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
        vda    253:0    0   40G  0 disk
        └─vda1 253:1    0   40G  0 part /
        vdb    253:16   0  100G  0 disk
        └─vdb1 253:17   0  100G  0 part

    In the command output, /dev/vdb1 is the partition you created.

11. Run the following command to set the file system format for the new partition:

    mkfs -t File system format /dev/vdb1

    In this example, run the following command to set the ext4 file system 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, 26213888 blocks
        1310694 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.

    The partition sizes supported by file systems vary. Therefore, you are advised to choose an appropriate file system based on your service requirements.

12. Run the following command to create a mount point:

    mkdir Mount point

    In this example, run the following command to create the /mnt/sdc mount point:

    mkdir /mnt/sdc

13. Run the following command to mount the new partition on the created mount point:

    mount Disk partition Mount point

    In this example, run the following command to mount the new partition /dev/vdb1 on /mnt/sdc:

    mount /dev/vdb1 /mnt/sdc

14. Run the following command to view 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  9.0M  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

    New partition /dev/vdb1 is mounted on /mnt/sdc.

    If the server is restarted, the mounting will become invalid. You can set automatic mounting for partitions at system start by modifying the /etc/fstab file. For details, see Setting Automatic Mounting at System Start.

#### Setting Automatic Mounting at System Start

Modify the fstab file to set automatic disk mounting at server start. You can also set automatic mounting for the servers containing data. This operation will not affect the existing data.

The following procedure shows how to set automatic disk mounting at server start by using UUIDs to identify disks in the fstab file. You are advised not to use device names to identify disks in the file because a device name may change (for example, from /dev/vdb1 to /dev/vdb2) during the server stop or start, resulting in improper server running after restart.

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

1. Run the following command to query the partition UUID:

   blkid Disk partition

   In this example, run the following command to query the UUID of the /dev/vdb1 partition:

   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"

   The UUID of the /dev/vdb1 partition is displayed.

2. Run the following command to open the fstab file using the vi editor:

   vi /etc/fstab

3. Press i to enter the 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. Perform the following operations to verify the automatic mounting function:

   1. Run the following command to unmount the partition:

      umount Disk partition

      In this example, run the following command:

      umount /dev/vdb1

   2. Run the following command to reload all the content in the /etc/fstab file:

      mount -a

   3. Run the following command to 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, the automatic mounting function takes effect:

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

Parent topic: Initializing EVS Data Disks