# What Are the Requirements for Attaching an EVS Disk to an ECS?

- The EVS disk and the target ECS must be located in the same AZ.
- For a non-shared disk, the EVS disk must be in Available state.

  For a shared disk, the target EVS disk must be in In-use or Available state.

- The target ECS must be in Running or Stopped state.
- A SCSI EVS disk cannot be used as an ECS system disk.
- Certain ECSs support SCSI EVS disk attachment. For details, see Which ECSs Can Be Attached with SCSI EVS Disks?

Parent topic: Disk Management