Initializing a Linux Data Disk (Using Parted)
Scenarios
This section uses CentOS 7.0 64-bit as an example to describe how to initialize a data disk attached to a Linux BMS and use Parted to partition the data disk.
The method for initializing a disk varies depending on the OSs running on the server. This document is for reference only. For detailed operations and differences, see the product documents of the OSs running on the corresponding BMSs.
Prerequisites
- You have logged in to the BMS as user root. For details, see section "Logging In to a Linux BMS" in Bare Metal Server User Guide.
- A data disk has been attached to the BMS and has not been initialized.
Creating Partitions and Mounting a Disk
The following example shows you how to use Parted to create a partition on a new data disk that has been attached to the BMS. The default partitioning style is GPT and the default file system format is ext4. Mount the file system to /mnt/sdc, and configure automatic mounting upon system start.
- Run the following command to view information about the added 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
This command output indicates that the BMS contains two disks. /dev/xvda is used as the system disk, and /dev/xvdb is the newly added data disk.
- Run the following command to use 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.
- 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.
- 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: (The disk partition styles include MBR and GPT.)
mklabel gpt
NOTICE:
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.
- 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
- Enter unit s and press Enter to set the measurement unit of the disk to sector numbers.
- Enter mkpart opt 2048s 100% and press Enter. In this example, one partition is created for the added data disk.
2048s indicates the initial disk capacity, and 100%indicates the final disk capacity. 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? Cancel
If the preceding warning message is displayed, enter Cancel to stop partitioning. Then, find the first sector with the best disk performance and use that value to partition the disk. In this example, the first sector with the best disk performance is 2048s. Therefore, the system does not display the warning message.
- 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.
- Enter q and press Enter to exit Parted.
- Run the following command to view information about partitioning:
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.
- Run the following command to set the file system format of the created partition:
mkfs -t File system format /dev/xvdb1
For example, run the following command to set the file system format to ext4:
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. Wait for the system running, and do not exit.
NOTICE:
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 mounting point:
mkdir Mounting point
For example, run the following command to create a mounting point /mnt/sdc:
mkdir /mnt/sdc
- Run the following command to mount the new partition to the mounting point created in 12.
mount /dev/xvdb1 Mounting point
For example, run the following command to mount the created partition to /mnt/sdc:
mount /dev/xvdb1 /mnt/sdc
- Run the following command to check the mounting 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 new partition /dev/xvdb1 is mounted to /mnt/sdc.
Setting Automatic Disk Mounting at System Start
To automatically mount a disk when a BMS starts, you should not specify its partition, for example /dev/xvdb1, in /etc/fstab. This is because the sequence of cloud devices may change during the BMS stop and start. For example, /dev/xvdb1 may change to /dev/xvdb2. You are advised to use the UUID to automatically mount data disks.
NOTE:
The 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
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.
- Run the following command to open the fstab file using the vi editor:
vi /etc/fstab
- Press i to enter the editing mode.
- 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
- Press Esc, enter :wq, and press Enter.
The system saves the configurations and exits the vi editor.
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