How to Detach a Disk from a Linux Virtual Machine

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Important

Classic VMs will be retired on March 1, 2023.

If you use IaaS resources from ASM, please complete your migration by March 1, 2023. We encourage you to make the switch sooner to take advantage of the many feature enhancements in Azure Resource Manager.

For more information, see Migrate your IaaS resources to Azure Resource Manager by March 1, 2023.

Note

Azure has two different deployment models for creating and working with resources: Resource Manager and Classic. This article covers using the Classic deployment model. Microsoft recommends that most new deployments use the Resource Manager model.

When you no longer need a data disk that's attached to a virtual machine (VM), you can easily detach it. When you detach a disk from the VM, the disk is not removed it from storage. If you want to use the existing data on the disk again, you can reattach it to the same VM, or another one.

Note

A VM in Azure uses different types of disks - an operating system disk, a local temporary disk, and optional data disks. For details, see About Disks and VHDs for Virtual Machines. You cannot detach an operating system disk unless you also delete the VM.

Find the disk

Before you can detach a disk from a VM you need to find out the LUN number, which is an identifier for the disk to be detached. To do that, follow these steps:

  1. Open Azure CLI and connect to your Azure subscription. Make sure you are in Azure Service Management mode (azure config mode asm).

  2. Find out which disks are attached to your VM. The following example lists disks for the VM named myVM:

    azure vm disk list myVM

    The output is similar to the following example:

    * Fetching disk images
* Getting virtual machines
* Getting VM disks
  data:    Lun  Size(GB)  Blob-Name                         OS
  data:    ---  --------  --------------------------------  -----
  data:         30        ubuntuVM-2645b8030676c8f8.vhd  Linux
  data:    0    30        myDataDisk.vhd
  info:    vm disk list command OK

  3. Note the LUN or the logical unit number for the disk that you want to detach.

Remove operating system references to the disk

Before detaching the disk from the Linux guest, you should make sure that all partitions on the disk are not in use. Ensure that the operating system does not attempt to remount them after a reboot. These steps undo the configuration you likely created when attaching the disk.

  1. Use the lsscsi command to discover the disk identifier. lsscsi can be installed by either yum install lsscsi (on Red Hat based distributions) or apt-get install lsscsi (on Debian based distributions). You can find the disk identifier you are looking for by using the LUN number. The last number in the tuple in each row is the LUN. In the following example from lsscsi, LUN 0 maps to /dev/sdc

    [1:0:0:0]    cd/dvd  Msft     Virtual CD/ROM   1.0   /dev/sr0
[2:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sda
[3:0:1:0]    disk    Msft     Virtual Disk     1.0   /dev/sdb
[5:0:0:0]    disk    Msft     Virtual Disk     1.0   /dev/sdc

  2. Use fdisk -l <disk> to discover the partitions associated with the disk to be detached. The following example shows the output for /dev/sdc:

    Disk /dev/sdc: 1098.4 GB, 1098437885952 bytes, 2145386496 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: 0x5a1d2a1a

    Device Boot      Start         End      Blocks   Id  System
/dev/sdc1            2048  2145386495  1072692224   83  Linux

  3. Unmount each partition listed for the disk. The following example unmounts /dev/sdc1:

    sudo umount /dev/sdc1

  4. Use the blkid command to discovery the UUIDs for all partitions. The output is similar to the following example:

    /dev/sda1: UUID="11111111-1b1b-1c1c-1d1d-1e1e1e1e1e1e" TYPE="ext4"
/dev/sdb1: UUID="22222222-2b2b-2c2c-2d2d-2e2e2e2e2e2e" TYPE="ext4"
/dev/sdc1: UUID="33333333-3b3b-3c3c-3d3d-3e3e3e3e3e3e" TYPE="ext4"

  5. Remove entries in the /etc/fstab file associated with either the device paths or UUIDs for all partitions for the disk to be detached. Entries for this example might be:

    UUID=33333333-3b3b-3c3c-3d3d-3e3e3e3e3e3e   /datadrive   ext4   defaults   1   2

    or

    /dev/sdc1   /datadrive   ext4   defaults   1   2

Detach the disk

After you find the LUN number of the disk and removed the operating system references, you're ready to detach it:

  1. Detach the selected disk from the virtual machine by running the command azure vm disk detach <virtual-machine-name> <LUN>. The following example detaches LUN 0 from the VM named myVM:

    azure vm disk detach myVM 0

  2. You can check if the disk got detached by running azure vm disk list again. The following example checks the VM named myVM:

    azure vm disk list myVM

    The output is similar to the following example, which shows the data disk is no longer attached:

    info:    Executing command vm disk list

* Fetching disk images
* Getting virtual machines
* Getting VM disks
 data:    Lun  Size(GB)  Blob-Name                         OS
 data:    ---  --------  --------------------------------  -----
 data:         30        ubuntuVM-2645b8030676c8f8.vhd  Linux
 info:    vm disk list command OK

The detached disk remains in storage but is no longer attached to a virtual machine.

Next steps

You can read more about using your Linux VM in the following articles: