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 Introduction to Data Disk Initialization Scenarios and Partition Styles.
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.
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.
- 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.
- 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):
- 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.
If MBR is used, a maximum of four primary partitions, or three primary partitions plus one extended partition can be created. The extended partition must be divided into logical partitions before use.
Disk partitions created using GPT are not categorized.
- 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.
- 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 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.
- 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.
In case that you want to discard the changes made before, you can exit fdisk by entering q.
- Synchronize the new partition table to the OS.
partprobe
- 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: doneThe formatting takes a period of time. Observe the system running status and do not exit.
The partition sizes supported by file systems vary. Choose an appropriate file system format based on your service requirements.
- Create a mount point.
mkdir Mount point
In this example, the /mnt/sdc mount point is created.
mkdir /mnt/sdc
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.
- 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
- 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.
After the server is restarted, the disk will not be automatically mounted. You can modify the /etc/fstab file to configure automount at startup. 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 server stop or start. This can even prevent the server from booting up.
UUIDs are the unique character strings for identifying partitions in Linux.
- 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.
- 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
- Press Esc, enter :wq, and press Enter.
The system saves the configurations and exits the vi editor.
- Verify that the disk is auto-mounted at startup.
- Unmount the partition.
In this example, run the following command:
umount /dev/vdb1
- Reload all the content in the /etc/fstab file.
mount -a
- Query the file system mounting information.
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)
- Unmount the partition.