Format and mount a non-boot disk on a Linux VM

If you attached a new, blank disk to your VM, before you can use it you must format and mount the disk. If you attached a disk that already contains data, then you must mount the disk before you can use it.

Before you begin

  • If you haven't already, set up authentication. Authentication is the process by which your identity is verified for access to Google Cloud services and APIs. To run code or samples from a local development environment, you can authenticate to Compute Engine as follows.

    Select the tab for how you plan to use the samples on this page:


    When you use the Google Cloud console to access Google Cloud services and APIs, you don't need to set up authentication.


    1. Install the Google Cloud CLI, then initialize it by running the following command:

      gcloud init
    2. Set a default region and zone.


    To use the REST API samples on this page in a local development environment, you use the credentials you provide to the gcloud CLI.

      Install the Google Cloud CLI, then initialize it by running the following command:

      gcloud init

    For more information, see Authenticate for using REST in the Google Cloud authentication documentation.

Connect to the VM

  1. Go to the VM instances page.

    Go to the VM instances page

  2. Click the SSH button next to the instance that has the new attached disk. The browser opens a terminal connection to the VM.

Format a non-boot disk on a Linux VM

  1. In the terminal, use the symlink created for your attached disk to determine which device to format.

     ls -l /dev/disk/by-id/google-*

    Unformatted disks don't have additional symlinks with -partN in the name.

     google-extra-scsi-disk -> ../../sdb
     google-instance-2 -> ../../sda
     google-instance-2-part1 -> ../../sda1
     google-instance-2-part14 -> ../../sda14
     google-instance-2-part15 -> ../../sda15
     google-local-nvme-ssd-0 -> ../../nvme0n1
     google-local-nvme-ssd-1 -> ../../nvme0n2

    In this example, the new Persistent Disk was created with the name extra-scsi-disk. The device name for the new disk is sdb.

  2. Format the disk device using the mkfs tool. This command deletes all data from the specified disk, so make sure that you specify the disk device correctly.

    You can use any file format that you need, but we recommend a single ext4 file system without a partition table. You can increase the size of your disk later without having to modify disk partitions.

    To maximize disk performance, use the recommended formatting options with the -E flag. It is not necessary to reserve space for the root volume on this secondary disk, so specify -m 0 to use all of the available disk space.

     $ sudo mkfs.ext4 -m 0 -E lazy_itable_init=0,lazy_journal_init=0,discard /dev/DEVICE_NAME

    Replace DEVICE_NAME with the device name of the disk that you are formatting. For example, using the example output from the first step, you would use sdb for the device name.

    The command formats the entire disk with no partition table.

Mount the disk

  1. Create a directory that serves as the mount point for the new disk on the VM. You can use any directory. The following example creates a directory under /mnt/disks/.

    $ sudo mkdir -p /mnt/disks/MOUNT_DIR

    Replace MOUNT_DIR with the directory at which to mount disk.

  2. Use the mount tool to mount the disk to the instance, and enable the discard option:

    $ sudo mount -o discard,defaults /dev/DEVICE_NAME /mnt/disks/MOUNT_DIR

    Replace the following:

    • DEVICE_NAME: the device name of the disk to mount.
    • MOUNT_DIR: the directory in which to mount your disk.
  3. Configure read and write permissions on the disk. For this example, grant write access to the disk for all users.

    $ sudo chmod a+w /mnt/disks/MOUNT_DIR

    Replace MOUNT_DIR with the directory where you mounted your disk.

Configure automatic mounting on VM restart

Add the disk to your /etc/fstab file, so that the disk automatically mounts again when the VM restarts. On Linux operating systems, the device name can change with each reboot, but the device UUID always points to the same volume, even when you move disks between systems. Because of this, we recommend using the device UUID instead of the device name to configure automatic mounting on VM restart.

  1. Create a backup of your current /etc/fstab file.

    $ sudo cp /etc/fstab /etc/fstab.backup
  2. Use the blkid command to list the UUID for the disk.

    $ sudo blkid /dev/DEVICE_NAME
    /dev/DEVICE_NAME: UUID="a9e1c14b-f06a-47eb-adb7-622226fee060" BLOCK_SIZE="4096"
    TYPE="ext4" PARTUUID="593b3b75-108f-bd41-823d-b7e87d2a04d1"

    Replace the following:

    • DEVICE_NAME: the device name of the disk that you want to automatically mount. If you created a partition table on the disk, specify the partition that you want to mount by adding the suffix appended to the device name. For example, if sdb is the device name for the disk, sdb1 might be the name for the partition.
  3. Open the /etc/fstab file in a text editor and create an entry that includes the UUID. For example:

    UUID=UUID_VALUE /mnt/disks/MOUNT_DIR ext4 discard,defaults,MOUNT_OPTION 0 2

    Replace the following:

    • UUID_VALUE: the UUID of the disk, listed in the output of the previous step
    • MOUNT_DIR: the directory where you mounted your disk
    • MOUNT_OPTION: specifies what the operating system does if it cannot mount the zonal persistent disk at boot time. For valid values, see The fourth field in the Linux fstab documentation. To let the system boot even if the disk is unavailable, use the nofail mount option.
  4. Use the cat command to verify that your /etc/fstab entries are correct:

    $ cat /etc/fstab
    UUID=6B33-A686 /boot/efi vfat defaults 0 0
    UUID=UUID_VALUE /mnt/disks/MOUNT_DIR ext4 discard,defaults,MOUNT_OPTION 0 2

Always keep the /etc/fstab file in sync with the devices that are attached to a VM. If you want to detach a disk or create a snapshot from the boot disk for a VM, edit the /etc/fstab file and remove the entry for the disk. Even if you set MOUNT_OPTION to nofail or nobootwait, remove the entry before you create your boot disk snapshot or detach the disk.

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