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Amazon Elastic Compute Cloud
User Guide for Windows Instances

Paravirtual Drivers for Windows Server Instances

Windows AMIs contain a set of drivers to permit access to virtualized hardware. These drivers are used by Amazon EC2 to map instance store and Amazon EBS volumes to their devices. The following table shows key differences between the different drivers.

RedHat PV Citrix PV AWS PV

Instance type

Not supported for all instance types. If you specify an unsupported instance type, the instance is impaired.

Supported for all instance types.

Supported for all instance types.

Attached volumes

Supports up to 16 attached volumes.

Supports more than 16 attached volumes.

Supports more than 16 attached volumes.

Network

The driver has known issues where the network connection resets under high loads; for example, fast FTP file transfers.

The driver automatically configures jumbo frames on the network adapter when on a compatible instance type. When the instance is in a placement group, this offers better network performance between instances in the placement group.

The following list shows which PV drivers you should run on each version of Windows Server on Amazon EC2.

  • Windows Server 2003 and 2003 R2: Citrix PV 5.9

  • Windows Server 2008: Citrix PV 5.9

  • Windows Server 2008 R2: AWS PV

  • Windows Server 2012 and 2012 R2: AWS PV

  • Windows Server 2016: AWS PV

AWS PV Drivers

The AWS PV drivers are stored in the %ProgramFiles%\Amazon\Xentools directory. This directory also contains public symbols and a command line tool, xenstore_client.exe, that enables you to access entries in XenStore. For example, the following PowerShell command returns the current time from the Hypervisor:

Copy
PS C:\> [DateTime]::FromFileTimeUTC((gwmi -n root\wmi -cl AWSXenStoreBase).XenTime).ToString("hh:mm:ss") 11:17:00

The AWS PV driver components are listed in the Windows registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services. These driver components are as follows: XENBUS, xeniface, xennet, xenvbd, and xenvif.

AWS PV also has a driver component named LiteAgent, which runs as a Windows service. It handles tasks such as shutdown and restart events from the API. You can access and manage services by running Services.msc from the command line.

Installing the Latest AWS PV Drivers

Amazon Windows AMIs contain a set of drivers to permit access to virtualized hardware. These drivers are used by Amazon EC2 to map instance store and Amazon EBS volumes to their devices. We recommend that you install the latest drivers to improve stability and performance of your EC2 Windows instances.

Installation Options

AWS PV Driver Version History

The following table shows the changes to AWS PV drivers for each driver release.

Driver version Details Release date

7.4.6

Stability fixes to make AWS PV drivers more resilient.

26 April 2017

7.4.3

Added support for Windows Server 2016.

Stability fixes for all supported Windows OS versions.

18 Nov 2016

7.4.2

Stability fixes for support of X1 instance type.

2 Aug 2016

7.4.1

  • Performance improvement in AWS PV Storage driver.

  • Stability fixes in AWS PV Storage driver: Fixed an issue where the instances were hitting a system crash with bugcheck code 0x0000DEAD.

  • Stability fixes in AWS PV Network driver.

  • Added support for Windows Server 2008R2.

12 July 2016

7.3.2

  • Improved logging and diagnostics.

  • Stability fix in AWS PV Storage driver. In some cases disks may not surface in Windows after reattaching the disk to the instance.

  • Added support for Windows Server 2012.

24 June 2015

7.3.1

TRIM update: Fix related to TRIM requests. This fix stabilizes instances and improves instance performance when managing large numbers of TRIM requests.

7.3.0

TRIM support: The AWS PV driver now sends TRIM requests to the hypervisor. Ephemeral disks will properly process TRIM requests given the underlying storage supports TRIM (SSD). Note that EBS-based storage does not support TRIM as of March 2015.

7.2.5

  • Stability fix in AWS PV Storage drivers: In some cases the AWS PV driver could dereference invalid memory and cause a system failure.

  • Stability fix while generating a crash dump: In some cases the AWS PV driver could get stuck in a race condition when writing a crash dump. Before this release, the issue could only be resolved by forcing the driver to stop and restart which lost the memory dump.

7.2.4

Device ID persistence: This driver fix masks the platform PCI device ID and forces the system to always surface the same device ID, even if the instance is moved. More generally, the fix affects how the hypervisor surfaces virtual devices. The fix also includes modifications to the co-installer for the AWS PV drivers so the system persists mapped virtual devices.

7.2.2

  • Load the AWS PV drivers in Directory Services Restore Mode (DSRM) mode: Directory Services Restore Mode is a safe mode boot option for Windows Server domain controllers.

  • Persist device ID when virtual network adapter device is reattached: This fix forces the system to check the MAC address mapping and persist the device ID. This fix ensures that adapters retain their static settings if the adapters are reattached.

7.2.1

  • Run in safe mode: Fixed an issue where the driver would not load in safe mode. Previously the AWS PV Drivers would only instantiate in normal running systems.

  • Add disks to Microsoft Windows Storage Pools: Previously we synthesized page 83 queries. The fix disabled page 83 support. Note this does not affect storage pools that are used in a cluster environment because PV disks are not valid cluster disks.

7.2.0

Base: The AWS PV base version.

Citrix PV Drivers

The Citrix PV drivers are stored in the %ProgramFiles%\Citrix\XenTools (32-bit instances) or %ProgramFiles(x86)%\Citrix\XenTools (64-bit instances) directory.

The Citrix PV driver components are listed in the Windows registry under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\services. These driver components are as follows: xenevtchn, xeniface, xennet, Xennet6, xensvc, xenvbd, and xenvif.

Citrix also has a driver component named XenGuestAgent, which runs as a Windows service. It handles tasks such as time synchronization at boot (Windows Server 2003 only), and shutdown and restart events from the API. You can access and manage services by running Services.msc from the command line.

If you are encountering networking errors while performing certain workloads, you may need to disable the TCP offloading feature for the Citrix PV driver. For more information, see TCP Offloading.

RedHat PV Drivers

RedHat drivers are supported for legacy instances, but are not recommended on newer instances with more than 12GB of RAM due to driver limitations. Instances with more than 12GB of RAM running RedHat drivers can fail to boot and become inaccessible. We recommend upgrading RedHat drivers to Citrix PV drivers, and then upgrade Citrix PV drivers to AWS PV drivers.

The source files for the RedHat drivers are in the %ProgramFiles%\RedHat (32-bit instances) or %ProgramFiles(x86)%\RedHat (64-bit instances) directory. The two drivers are rhelnet, the RedHat Paravirtualized network driver, and rhelscsi, the RedHat SCSI miniport driver.

Subscribing to Notifications

Amazon SNS can notify you when new versions of EC2 Windows Drivers are released. Use the following procedure to subscribe to these notifications.

To subscribe to EC2 notifications

  1. Open the Amazon SNS console at https://console.aws.amazon.com/sns/v2/home.

  2. In the navigation bar, change the region to US East (N. Virginia), if necessary. You must select this region because the SNS notifications that you are subscribing to are in this region.

  3. In the navigation pane, choose Subscriptions.

  4. Choose Create subscription.

  5. In the Create subscription dialog box, do the following:

    1. For TopicARN, copy the following Amazon Resource Name (ARN):

      arn:aws:sns:us-east-1:801119661308:ec2-windows-drivers

    2. For Protocol, choose Email.

    3. For Endpoint, type an email address that you can use to receive the notifications.

    4. Choose Create subscription.

  6. You'll receive a confirmation email. Open the email and follow the directions to complete your subscription.

Whenever new EC2 Windows drivers are released, we send notifications to subscribers. If you no longer want to receive these notifications, use the following procedure to unsubscribe.

To unsubscribe from Amazon EC2 Windows driver notification

  1. Open the Amazon SNS console at https://console.aws.amazon.com/sns/v2/home.

  2. In the navigation pane, choose Subscriptions.

  3. Select the checkbox for the subscription and then choose Actions, Delete subscriptions. When prompted for confirmation, choose Delete.