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 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.
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 with automatic mounting at system start.
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, the server contains two disks. /dev/vda is the system disk, and /dev/vdb is the new data disk.
Run the following command to enter 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):
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.
In this example, a primary partition is created. Therefore, enter p and press Enter to create a primary partition.
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.
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.
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.
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.
Enter p and press Enter to view details about the new partition.
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.
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.
Run the following command to synchronize the new partition table to the OS:
partprobe
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, 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. Therefore, you are advised to choose an appropriate file system based on your service requirements.
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
Note
The /mnt directory exists on all Linux systems. If the mount point fails to create, it may be that the /mnt directory has been accidentally deleted. Run the mkdir -p /mnt/sdc command to create the mount point.
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
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 9.1M 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
New partition /dev/vdb1 is mounted on /mnt/sdc.
Note
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.
Note
UUID is the unique character string for disk partitions in a Linux system.
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.
Run the following command to open the fstab file using the vi editor:
vi /etc/fstab
Press i to enter editing mode.
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
The preceding content is used for reference only. Add the information that is used in the environment. The parameters are described as follows:
The first column indicates the partition UUID obtained in 1.
The second column indicates the directory on which the partition is mounted. You can query the mount point using the df -TH command.
The third column indicates the file system format of the partition. You can query the file system format using the df -TH command.
The fourth column indicates the partition mount option. Normally, this parameter is set to defaults.
The fifth column indicates the Linux dump backup option.
0: Linux dump backup is not used. Normally, dump backup is not used, and you can set this parameter to 0.
1: Linux dump backup is used.
The sixth column indicates the fsck option, that is, whether to use fsck to check the attached disk during startup.
0: not use fsck.
If the mount point is the root partition (/), this parameter must be set to 1.
When this parameter is set to 1 for the root partition, this parameter for other partitions must start with 2 because the system checks the partitions in the ascending order of the values.
Press Esc, enter :wq, and press Enter.
The system saves the configurations and exits the vi editor.
Perform the following operations to verify the automatic mounting function:
Run the following command to unmount the partition:
umount Disk partition
In this example, run the following command:
umount /dev/vdb1
Run the following command to reload all the content in the /etc/fstab file:
mount -a
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, automatic mounting has been configured:
root@ecs-test-0001 ~]# mount | grep /mnt/sdc /dev/vdb1 on /mnt/sdc type ext4 (rw,relatime,data=ordered)