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Amazon Elastic Compute Cloud
User Guide for Windows Instances

Device Naming on Windows Instances

When you attach a volume to your instance, you include a device name for the volume. This device name is used by Amazon EC2. The block device driver for the instance assigns the actual volume name when mounting the volume, and the name assigned can be different from the name that Amazon EC2 uses.

For information about device names on Linux instances, see Device Naming on Linux Instances in the Amazon EC2 User Guide for Linux Instances.

Available Device Names

The following table lists the available device names for Windows instances. The number of volumes that you can attach to your instance is determined by the operating system. For more information, see Instance Volume Limits.

Driver Type Available Reserved for Root Recommended for EBS Volumes Instance Store Volumes NVMe Volumes

AWS PV, Citrix PV

xvd[b-z]

xvd[b-c][a-z]

/dev/sda1

/dev/sd[b-e]

/dev/sda1

xvd[f-z] †

xvd[a-e]

xvdc[a-x] (hs1.8xlarge)

/dev/nvme[0-26]n1 *

Red Hat PV

xvd[a-z]

xvd[b-c][a-z]

/dev/sda1

/dev/sd[b-e]

/dev/sda1

xvd[f-p]

xvd[a-e]

xvdc[a-x] (hs1.8xlarge)

/dev/nvme[0-26]n1 *

† If you map an EBS volume with the name xvda, Windows does not recognize the volume.

* NVMe instance store volumes are automatically enumerated and assigned a Windows drive letter. There is no need to specify NVMe instance store volumes in your block device mapping.

For more information about instance store volumes, see Amazon EC2 Instance Store.

Device Name Considerations

Keep the following in mind when selecting a device name:

  • Although you can attach your EBS volumes using the device names used to attach instance store volumes, we strongly recommend that you don't because the behavior can be unpredictable.

  • Amazon EC2 Windows AMIs come with an additional service installed, the Ec2Config Service. The Ec2Config service runs as a local system and performs various functions to prepare an instance when it first boots up. After the devices have been mapped with the drives, the Ec2Config service then initializes and mounts the drives. The root drive is initialized and mounted as C:\. The instance store volumes that come attached to the instance are initialized and mounted as Z:\, Y:\, and so on. By default, when an EBS volume is attached to a Windows instance, it can show up as any drive letter on the instance. You can change the settings of the Ec2Config service to set the drive letters of the EBS volumes per your specifications. For more information, see Configuring a Windows Instance Using the EC2Config Service and Mapping Disks to Volumes on Your Windows Instance.

  • The number of NVMe instance store volumes for an instance depends on the size of the instance. The device names are /dev/nvme0n1, /dev/nvme1n1, and so on.