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  6. Initializing a Linux Data Disk (parted)

Initializing a Linux Data Disk (parted)

Scenarios

This topic uses CentOS 7.0 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 greater than 2 TB. In Linux OSs, if the GPT partition style is used, the fdisk partitioning tool cannot be used. The parted partitioning tool must be used. For details about disk partition styles, see Scenarios and Disk Partitions.

The method for initializing an EVS 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 OSs running on the corresponding servers.

Prerequisites

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

Creating Partitions and Mounting a Disk

The following example shows you how new partitions can be created on a new data disk that has been attached to a server. The partitions will be created using parted, and GPT is used as the partition style. Furthermore, the partitions 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 added data disk:

    lsblk

    Information similar to the following is displayed:

    [root@ecs-centos-70 linux]# lsblk
    NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
    xvda    202:0    0   40G  0 disk 
    ├─xvda1 202:1    0    4G  0 part [SWAP]
    └─xvda2 202:2    0   36G  0 part /
    xvdb    202:16   0  10G  0 disk

    In the command output, the server contains two disks. /dev/xvda is the system disk, and /dev/xvdb is the added data disk.

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

    parted Added data disk

    In this example, /dev/xvdb is the added data disk.

    parted /dev/xvdb

    Information similar to the following is displayed:

    [root@ecs-centos-70 linux]# parted /dev/xvdb
    GNU Parted 3.1
    Using /dev/xvdb
    Welcome to GNU Parted! Type 'help' to view a list of commands.

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

    Information similar to the following is displayed:

    (parted) p
    Error: /dev/xvdb: unrecognised disk label
    Model: Xen Virtual Block Device (xvd)                                     
    Disk /dev/xvdb: 10.7GB
    Sector size (logical/physical): 512B/512B
    Partition Table: unknown
    Disk Flags:   

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

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

    mklabel Disk partition style

    For example, run the following command to set the partition style to GPT: (Disk partition styles include MBR and GPT.)

    mklabel gpt

    The maximum disk capacity supported by MBR is 2 TB, and that supported by GPT is 18 EB. Currently, an EVS data disk supports up to 32 TB. Therefore, use the GPT partition style if your disk capacity is greater than 2 TB.

    If you change the disk partition style after the disk has been used, the original 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: Xen Virtual Block Device (xvd)
    Disk /dev/xvdb: 20971520s
    Sector size (logical/physical): 512B/512B
    Partition Table: gpt
    Disk Flags: 
    
    Number  Start  End  Size  File system  Name  Flags

  6. Enter unit s and press Enter to set the measurement unit of the disk to sector numbers.
  7. Enter mkpart opt 2048s 100% and press Enter.

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

    Information similar to the following is displayed:
    (parted) mkpart opt 2048s 100%
    Warning: The resulting partition is not properly aligned for best performance.
    Ignore/Cancel? Ignore 

    If the preceding warning message is displayed, enter Ignore to ignore the performance warning.

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

    Information similar to the following is displayed:

    (parted) p                                                                
    Model: Xen Virtual Block Device (xvd)
    Disk /dev/xvdb: 20971520s
    Sector size (logical/physical): 512B/512B
    Partition Table: gpt
    Disk Flags: 
    
    Number  Start   End        Size       File system  Name  Flags
     1      2048s   20969471s  20967424s               opt

    Details about the /dev/xvdb1 partition are displayed.

  9. Enter q and press Enter to exit parted.
  10. Run the following command to view the disk partition information:

    lsblk

    Information similar to the following is displayed:

    [root@ecs-centos-70 linux]# lsblk                                 
    NAME    MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
    xvda    202:0    0   40G  0 disk 
    ├─xvda1 202:1    0    4G  0 part [SWAP]
    └─xvda2 202:2    0   36G  0 part /
    xvdb    202:16   0  100G  0 disk 
    └─xvdb1 202:17   0  100G  0 part 

    In the command output, /dev/xvdb1 is the partition you created.

  11. Run the following command to set the format for the file system of the newly created partition:

    mkfs -t File system format /dev/xvdb1

    For example, run the following command to set the ext4 file system for the /dev/xvdb1 partition:

    mkfs -t ext4 /dev/xvdb1

    Information similar to the following is displayed:

    [root@ecs-centos-70 linux]# mkfs -t ext4 /dev/xvdb1
    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
    655360 inodes, 2620928 blocks
    131046 blocks (5.00%) reserved for the super user
    First data block=0
    Maximum filesystem blocks=2151677925
    80 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
    
    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

    For 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 /dev/xvdb1 Mount point

    For example, run the following command to mount the newly created partition on /mnt/sdc:

    mount /dev/xvdb1 /mnt/sdc

  14. Run the following command to view the mount result:

    df -TH

    Information similar to the following is displayed:

    [root@ecs-centos-70 linux]# df -TH
    Filesystem     Type      Size  Used Avail Use% Mounted on
    /dev/xvda2     xfs        39G  4.0G   35G  11% /
    devtmpfs       devtmpfs  946M     0  946M   0% /dev
    tmpfs          tmpfs     954M     0  954M   0% /dev/shm
    tmpfs          tmpfs     954M  9.1M  945M   1% /run
    tmpfs          tmpfs     954M     0  954M   0% /sys/fs/cgroup
    /dev/xvdb1     ext4      11G   38M  101G   1% /mnt/sdc

    The newly created /dev/xvdb1 is mounted on /mnt/sdc.

Setting Automatic Disk Mounting at System Start

To automatically mount a disk when a server starts, you should not specify its partition, for example /dev/xvdb1, in /etc/fstab. Because the sequence of cloud devices, and therefore their names may change during the server stop and start. You are advised to use the universally unique identifier (UUID) in /etc/fstab to automatically mount a disk at system start.

NOTE:

The 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

    For example, run the following command to query the UUID of /dev/xvdb1:

    blkid /dev/xvdb1

    Information similar to the following is displayed:

    [root@ecs-b656 test]# blkid /dev/xvdb1
    /dev/xvdb1: UUID="1851e23f-1c57-40ab-86bb-5fc5fc606ffa" TYPE="ext4"

    The UUID of /dev/xvdb1 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=1851e23f-1c57-40ab-86bb-5fc5fc606ffa /mnt/sdc      ext4 defaults     0   2

  5. Press Esc, enter :wq, and press Enter.

    The system saves the configurations and exits the vi editor.