# Why Can't I Detach My Disk?

EVS disks can be used as system disks or data disks, but the way you detach each one is different.

- System disks: A system disk can only be detached offline. You must first stop the server that uses this system disk and then detach the disk.

  In Linux, a system disk is typically mounted on /dev/vda. In Windows, a system disk is normally Volume (C:).

- Data disks: A data disk can be detached regardless of whether it is offline or online.

  In Linux, a data disk is typically mounted on a mount point other than /dev/vda. In Windows, a data disk is normally a volume other than Volume (C:).

  - Offline: The server must be in the Stopped state. If it is not, stop the server and then detach the data disk.
  - Online: Some OSs support online detachment. In this case, you do not need to stop the server before detaching the data disk. For more information, see Storage > Detaching an EVS Disk from a Running ECS in the Elastic Cloud Server User Guide.

Parent topic: Detachment