Initializing a Linux Data Disk (Less Than or Equal to 2 TiB)

Scenarios

This section describes how to initialize a Linux data disk manually. The operations may vary depending on the server OS. Perform initialization operations based on your server OS.

**Table 1** Initialization instructions
Operation Instruction	OS	Partition Style	File System Format	Partitioning Tool	Example Configuration
Initializing a Data Disk Manually	Not limited	GPT MBR	ext* (such as ext2, ext3, and ext4), xfs, and btrfs	fdisk parted	Partitioning tool: fdisk Device name: /dev/vdb File system format: ext4 Mount points: /mnt/sdc and /mnt/sdd Partition 1: /dev/vdb1 Size: 40 GiB Partition style: MBR Partition 2: /dev/vdb2 Size: 60 GiB Partition style: MBR

Prerequisites

You have attached the disk to a server.
You are advised to back up the disk data before re-initializing a disk, because data may be lost after a disk is re-initialized.
You have logged in to the server.
- For how to log in to an ECS, see Logging In to an ECS.
- For how to log in to a BMS, see Logging In to a BMS.

Notes and Constraints

A disk created from a data source does not need to be initialized. Such a disk contains the source data in the beginning. Initializing the disk may clear the initial data on it.
Initializing a disk does not delete the snapshots created for the disk, so you can still use snapshots to roll back data to the source disk after the disk is initialized.

Initializing a Data Disk Manually

MBR supports a maximum of four primary partitions or a maximum of three primary partitions plus one extended partition. Multiple logical partitions can be created in the extended partition.

For example, if you want to create four partitions, you have the following options:

Create four primary partitions.
Create one primary partition and one extended partition (three logical partitions).
Create two primary partitions and one extended partition (two logical partitions).
Create three primary partitions and one extended partition (one logical partition).

The following example shows you how to use fdisk to create two primary MBR partitions (/dev/vdb1: 40 GiB; /dev/vdb2: 60 GiB) on the /dev/vdb data disk.

Log in to the server and create two primary partitions, /dev/vdb1 and /dev/vdb2 for data disk /dev/vdb.
1. Check that the capacity of the /dev/vdb data disk is 100 GiB.
  lsblk
```
[root@ecs-centos76 ~]# lsblk
NAME   MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
vda    253:0    0  40G  0 disk
├vda1 253:1    0   1G  0 part /boot
└vda2 253:2    0  39G  0 part /
vdb    253:16   0  100G 0 disk
```
1. Create the first primary partition /dev/vdb1.
  fdisk /dev/vdb
  
  n
  p
```
[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): n
Partition type:
   p   primary (0 primary, 0 extended, 4 free)
   e   extended
Select (default p): p
Partition number (1-4, default 1): 1
```
  Entering p for Partition type creates a primary partition, and entering e creates an extended partition.
  
  Set First sector to 2048 and Last sector to 83886079 for partition /dev/vdb1 (40 GiB).
```
First sector (2048-209715199, default 2048): 2048
Last sector, +sectors or +size{K,M,G} (2048-209715199, default 209715199):83886079
Partition 1 of type Linux and of size 40 GB is set
```
1. Create the second primary partition /dev/vdb2.
  n
  
  p
```
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 2): 2
```
  Set the First sector to 83886080 and Last sector to 209715199 for partition /dev/vdb2.
```
First sector (83886080-209715199, default 83886080): 83886080
Last sector, +sectors or +size{K,M,G} (83886080-209715199, default 209715199):209715199
Partition 2 of type Linux and of size 60 GB is set
```
  First and last sectors of the partitions in this example are calculated as follows:
  
  Sector value = Capacity/512 bytes, 1 GiB = 1073741824 bytes
  - First sector (2048-209715199, default 2048) shows the sector value range of the /dev/vdb data disk (100 GiB).
    First sector = 2048
    
    Last sector = Sector value – 1 = (100 x 1073741824/512) – 1 = 209715200 – 1=209715199
  - For the first partition /dev/vdb1 (40 GiB) of the /dev/vdb data disk:
    First sector = 2048 (The start sector of the /dev/vdb data disk is used.)
    
    Last sector = Sector value – 1 = (40 x 1073741824/512) – 1 = 83886079
  - For the second partition /dev/vdb2 (60 GiB) of the /dev/vdb data disk:
    First sector = Last sector of /dev/vdb1 + 1 = 83886079 + 1 = 83886080
    
    Last sector = First sector + Sector value – 1 = 83886080 + (60 x 1073741824/512) – 1 = 209715199

Check the sizes and partition styles of the new partitions.

Check whether the partitioning is successful.

Command (m for help): p

Disk /dev/vdb: 107.4 GB, 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: 0x994727e5

   Device Boot       Start         End      Blocks   Id  System
/dev/vdb1             2048    83886079    41942016   83  Linux
/dev/vdb2         83886080   209715199    62914560   83  Linux

Command (m for help):

In case that you want to discard the changes made before, you can exit fdisk by entering q and press Enter. Then, re-create the partitions by referring to step 1.

Write the changes to the partition table and synchronize the new partition table to the OS.
w

partprobe

If error message -bash: partprobe: command not found is returned, the system cannot identify the command. In this case, run yum install -y parted to install the command. Then run the command again.

Confirm that the partition style is MBR.

parted /dev/vdb

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

Number  Start   End      Size     Type     File system  Flags
 1      1049kB  42.9GB   42.9GB   primary
 2      42.9GB  107GB    64.4GB   primary             

(parted) q
[root@ecs-test-0001 ~]#

If Partition Table: msdos is returned, the partition style is MBR.

Enter q and press Enter to exit parted.

Create ext4 file systems for partitions /dev/vdb1 (40 GiB) and /dev/vdb2 (60 GiB).

mkfs -t ext4 /dev/vdb1

mkfs -t ext4 /dev/vdb2

It takes some time to create file systems. Do not exit before the system returns the following information:

[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
2621440 inodes, 10485504 blocks
524275 blocks (5.00%) reserved for the super user
First data block=0
Maximum filesystem blocks=2157969408
320 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

Allocating group tables: done
Writing inode tables: done
Creating journal (32768 blocks): done
Writing superblocks and filesystem accounting information: done

Run parted /dev/vdb and enter p to check that the file system format is ext4.

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

Number  Start   End      Size     Type     File system  Flags
 1      1049kB  42.9GB   42.9GB   primary  ext4
 2      42.9GB  107GB    64.4GB   primary  ext4            

(parted) q
[root@ecs-test-0001 ~]#

Enter q and press Enter to exit parted.

Create directories (mount points) and mount the new partitions on the created mount points.
mkdir -p /mnt/sdc

mkdir -p /mnt/sdd

mount /dev/vdb1 /mnt/sdc

mount /dev/vdb2 /mnt/sdd

lsblk

View the mount results.
```
[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  40G  0 part /mnt/sdc
├vdb2 253:18   0  60G  0 part /mnt/sdd
```
You should now see that partitions /dev/vdb1 and /dev/vdb2 are mounted on /mnt/sdc and /mnt/sdd.

Use the partition UUIDs to configure auto mount at startup.

Mounts become invalid after a system reboot. You can configure auto mount at startup by adding information of the new partition into the /etc/fstab file.
You are advised not to use device names to identify disks in the /etc/fstab file because device names are assigned dynamically and may change (for example, from /dev/vdb1 to /dev/vdb2) after a stop or start. This can even prevent your server from booting up.
UUIDs are the unique character strings for identifying partitions in Linux.
This operation does not affect the existing data on the server.

Query the partition UUIDs.
blkid /dev/vdb1

blkid /dev/vdb2
```
[root@ecs-test-0001 ~]# blkid /dev/vdb1
/dev/vdb1: UUID="0b3040e2-1367-4abb-841d-ddb0b92693df" TYPE="ext4"
/dev/vdb2: UUID="0d6769k2-1745-9dsf-453d-hgd0b34267dj" TYPE="ext4"
```
The UUIDs of partitions /dev/vdb1 and /dev/vdb2 are 0b3040e2-1367-4abb-841d-ddb0b92693df and 0d6769k2-1745-9dsf-453d-hgd0b34267dj.

Configure auto mount at startup.

vi /etc/fstab

Press i to enter the editing mode, move the cursor to the end of the file, press Enter, and add the following content:

UUID=0b3040e2-1367-4abb-841d-ddb0b92693df    /mnt/sdc     ext4    defaults     0    2
UUID=0d6769k2-1745-9dsf-453d-hgd0b34267dj    /mnt/sdd     ext4    defaults     0    2

Press Esc, enter :wq, and press Enter to save the settings and exit the vi editor.

**Table 2** Parameter description
Example Value	Description
UUID=0b3040e2-1367-4abb-841d-ddb0b92693df	The UUID of the partition.
/mnt/sdc	The mount point of the partition.
ext4	The file system format of the partition.
defaults	The partition mount option. Normally, this parameter is set to defaults.
0	The Linux dump backup option. 0: Linux dump backup is not used. Usually, dump backup is not used, and you can set this parameter to 0. 1: Linux dump backup is used.
2	The fsck option, which means whether to use fsck to check the disk during startup. 2: The check starts from the partitions whose mount points are non-root directories. / is the root directory. 1: The check starts from the partitions whose mount points are root directories. 0: The fsck option is not used.

Verify that auto mount takes effect.
umount /dev/vdb1

umount /dev/vdb2

mount -a

The system reloads all the content in the /etc/fstab file.

Query file system mounting information.

mount | grep /mnt/sdc

mount | grep /mnt/sdd

If information similar to the following is displayed, auto mount has taken effect:
```
root@ecs-test-0001 ~]# mount | grep /mnt/sdc
/dev/vdb1 on /mnt/sdc type ext4 (rw,relatime,data=ordered)
root@ecs-test-0001 ~]# mount | grep /mnt/sdd
/dev/vdb2 on /mnt/sdd type ext4 (rw,relatime,data=ordered)
```