Device names on Windows instances - Amazon Elastic Compute Cloud

Device names 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.

The number of volumes that your instance can support is determined by the operating system. For more information, see Instance volume limits.

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

Windows AMIs use one of the following sets of drivers to permit access to virtualized hardware: AWS PV, Citrix PV, and RedHat PV. For more information, see Paravirtual drivers for Windows instances.

The following table lists the available device names that you can specify in a block device mapping or when attaching an EBS volume.

Driver type Available Reserved for root volume Recommended for EBS volumes Instance store volumes

AWS PV, Citrix PV

xvd[b-z]

xvd[b-c][a-z]

/dev/sda1

/dev/sd[b-e]

/dev/sda1

xvd[f-z] *

xvdc[a-x]

xvd[a-e]

**

Red Hat PV

xvd[a-z]

xvd[b-c][a-z]

/dev/sda1

/dev/sd[b-e]

/dev/sda1

xvd[f-p]

xvdc[a-x]

xvd[a-e]

* For Citrix PV and Red Hat PV, if you map an EBS volume with the name xvda, Windows does not recognize the volume (the volume is visible for AWS PV or AWS NVMe).

** NVMe instance store volumes are automatically enumerated and assigned a Windows drive letter.

For more information about instance store volumes, see Amazon EC2 instance store. For more information about NVMe EBS volumes (Nitro-based instances), including how to identify the EBS device, see Amazon EBS and NVMe in the Amazon EBS User Guide.

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.

  • The number of NVMe instance store volumes for an instance depends on the size of the instance. NVMe instance store volumes are automatically enumerated and assigned a Windows drive letter.

  • AWS Windows AMIs come with additional software that prepares an instance when it first boots up. This is either the EC2Config service (Windows AMIs prior to Windows Server 2016) or EC2Launch (Windows Server 2016 and later). After the devices have been mapped to drives, they are initialized and mounted. The root drive is initialized and mounted as C:\. 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 to set the drive letters of the volumes per your specifications. For instance store volumes, the default depends on the driver. AWS PV drivers and Citrix PV drivers assign instance store volumes drive letters going from Z: to A:. Red Hat drivers assign instance store volumes drive letters going from D: to Z:. For more information, see Configure a Windows instance using the EC2Config service (legacy), Configure a Windows instance using EC2Launch, and Map disks to volumes on your Windows instance.