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

After a newly created data disk is attached to a server, you must log in to the server and initialize the disk before you can use the disk. This section describes how to initialize a Linux data disk. The operations may vary depending on the server OS.

The maximum disk size that MBR supports is 2 TiB, and that GPT supports is 18 EiB. If your disk capacity is less than 2 TiB, you can use either the MBR or GPT partition style. However, if your disk is greater than 2 TiB or you may expand it to over 2 TiB later, use GPT when initializing disks.

The disk has been attached to a server. For how to attach disks, see Attaching an EVS Disk.

• 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. If you need to re-initialize the disk, you are advised to back up the disk data first. For how to back up data using CBR, see Backing Up EVS Disks. For how to back up data using snapshots, see Creating an EVS Snapshot.
• 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.

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

1. Log in to the server as user root.

   For how to log in to an ECS, see the Elastic Cloud Server User Guide.

2. Create partitions. In this example, 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   40G  0 part /
      vdb    253:16   0  100G 0 disk
      
      

      The command output shows that there are two EVS disks. /dev/vda is the system disk, and /dev/vdb is the new data disk, whose 100 GiB is not partitioned.

   2. Create the first primary partition /dev/vdb1 for /dev/vdb.

      fdisk /dev/vdb

      n

      p

      1

      [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. The default value is p.
      • Partition number indicates the partition serial number. Enter a value ranging from 1 to 4.
   3. Set First sector to 2048 and Last sector to 83886079 for partition /dev/vdb1 (40 GiB). For how to calculate the values, see Table 2.

      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
      
      

      Table 2 First and last sectors in this example are calculated as follows

      Sector	/dev/vdb1 (40 GiB)	/dev/vdb2 (60 GiB)	Formula for Calculating the Value of sectors
      First sector	2048 (The first sector of the /dev/vdb data disk is used.)	Last sector of /dev/vdb1 + 1 = 83886079 + 1 = 83886080	Value of sectors = Capacity × 1073741824/512
      Last sector	Value of sectors – 1 = (40 × 1073741824/512) – 1 = 83886079	First sector + Value of sectors – 1 = 83886080 + (60 × 1073741824/512) – 1 = 209715199

   4. Create the second primary partition /dev/vdb2 for /dev/vdb.

      n

      p

      2

      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 
      
      

   5. 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
      
      

   6. Check the sizes and partition styles of the new partitions.

      p

      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):
      
      

      Disk label type: dos indicates the MBR partition style.

   Note

   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 and step 2.

   7. Write the changes to the partition table.

      w

      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

      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.

   8. Synchronize the new partition table to the OS.

      partprobe

3. Create file systems.
   1. 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

      Note

      • mkfs -t <file-system-format> <disk-partition-name>: To create an xfs file system, the command is mkfs -t xfs <disk-partition-name>. To create a btrfs file system, the command is mkfs -t btrfs <disk-partition-name>.
      • 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
      
      

   2. Check whether the file system format is ext4.

      blkid /dev/vdb

      [root@ecs-test-0001 ~]#  blkid /dev/vdb 
      /dev/vdb1: UUID="0b3040e2-1367-4abb-841d-ddb0b92693df" TYPE="ext4"
      /dev/vdb2: UUID="0d6769k2-1745-9dsf-453d-hgd0b34267dj" TYPE="ext4"
      
      

4. Create directories (mount points) and mount the new partitions on the created mount points.
   1. Mount /dev/vdb1 on /mnt/sdc.

      mkdir -p /mnt/sdc

      mount /dev/vdb1 /mnt/sdc

   2. Mount /dev/vdb2 on /mnt/sdd.

      mkdir -p /mnt/sdd

      mount /dev/vdb2 /mnt/sdd

   3. View the mount results.

      lsblk

   [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.

5. (Optional) Use the partition UUIDs to configure auto mount at startup.

   UUIDs are the unique character strings for identifying partitions in Linux. Mounts become invalid after a system reboot. You can configure auto mount at startup by adding information of the new partitions into the /etc/fstab file.

   Note

   • 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 server stop or start. This can even prevent your server from booting up.
   • This operation will not affect the existing data on the ECS.
   1. Query the partition UUIDs.

      blkid /dev/vdb1

      blkid /dev/vdb2

      [root@ecs-test-0001 ~]#  blkid /dev/vdb 
      /dev/vdb1: UUID="0b3040e2-1367-4abb-841d-ddb0b92693df" TYPE="ext4"
      /dev/vdb2: UUID="0d6769k2-1745-9dsf-453d-hgd0b34267dj" TYPE="ext4"
      
      

      Take note of the partition UUIDs, which will be used in the next step. In this example, the partition UUIDs are 0b3040e2-1367-4abb-841d-ddb0b92693df and 0d6769k2-1745-9dsf-453d-hgd0b34267dj.

   2. 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 3 Content 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.

6. (Optional) Verify that auto mount takes effect.

   You can restart the server to check whether auto mount takes effect. Alternatively, you can perform the following steps to simulate auto mount.

   1. To verify auto mount, unmount the partitions first.

   umount /dev/vdb1

   umount /dev/vdb2

   2. Reload all the content in the /etc/fstab file. /etc/fstab is a static file system table that contains the list of file systems that need to be automatically mounted during system startup.

   mount -a

   3. Query the file system mount 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)
   
   

You can use parted to create either MBR or GPT partitions. The only difference is that the command used to set the partition style is different. All other operations are the same. For the initialization instructions with parted, see Initializing a Data Disk Using parted.

Commands for setting partition styles:

MBR:

GPT: