How the Image Store Works

  • Article

Applies To: Windows Server 2008

The image store stores the .wim images and helps the client computer obtain and install the images. The image store is a collection of image groups. An image group is a collection of images that share security options and file resources.

In This Topic

  • When Images Are Verified

  • How Images are Enumerated

  • How Images Are Compressed

  • How Images Are Captured

When Images Are Verified

Windows Deployment Services verifies each block of images to ensure that the source image file is not corrupt. The verification process compares the Secure Hash Algorithm (SHA-1) hashes of the image file with known good values from either a check block in the .wim file or the hashes of the actual files.

The types of images that Windows Deployment Services verifies are as follows:

  • Images that you create by using the Image Capture Wizard

  • Images that you add to the server

  • Images that you export (the external image file that was exported is verified)

  • Images that you replace on the server

How Images are Enumerated

Install images are enumerated between the Windows Deployment Services client and the image store. The following sequence of steps outlines this process.

  1. A remote procedure call (RPC) communication channel is established between the client and the server.

  2. Credentials are specified on the client computer (either manually or in an unattend file), and the user is authenticated.

  3. The server enumerates all .wim files within the image store, including .wim metadata, the folder that contains the .wim file, file name of the .wim file, and the access control list (ACL) of the file. Note that only files within the first level of the image group folder are enumerated; folders and subfolders are not enumerated. This shortens the time for the image enumeration and ensures that other .wim files (such as data .wim files in a $OEM$ folder structure) are not accidentally returned during the enumeration process.

  4. An authentication token is obtained by the server for the user who is logged on.

  5. Any ACLs that were found during enumeration are checked against the user.

  6. The server sends information for all images that the user has permissions to view back to the Windows Deployment Services client.

  7. The Windows Deployment Services client performs additional image filtering, if necessary.

  8. The list of available images is displayed to the user on the image selection page.

How Images Are Compressed

All images within an image group share the same compression type. The valid compression types are as follows: no compression, XPRESS (quick compression), and LZX (maximum compression). Although the decompression times are essentially equivalent for both the XPRESS and LZX types, the initial compression time (performed when the image is created) is longer for LZX. The following table shows the expected compression type for each action.

Action Expected compression type

Create an image group.

No compression type

Add the first image to an image group.

The same compression type as the image

Add subsequent images to an image group.

The same compression type as the image group

Export an image.

The current image group compression type

Append an image to an existing .wim file.

The same compression type as the .wim file

Create an install image by using the Image Capture Wizard.

Either LZX or XPRESS. The default compression type is XPRESS.

Create a new capture image.

LZX

Create a new discover image.

LZX

Convert a RIPREP image.

LZX

How Images Are Captured

The screens in the Image Capture Wizard walk you through the process of capturing the image, as described in the following sequence of steps.

  1. You boot the computer into the capture image.

  2. The Image Capture Wizard is started.

  3. The Image Capture Wizard searches for the WDSCapture.inf file in the X:\Windows\System32 folder.

    • If the file exists and contains settings, those settings are used.

    • If the file exists but settings for a particular section are missing, you must enter the missing information in the UI.

    • If the file does not exist, you must enter the missing information in the UI.

  4. The Image Capture Wizard scans all local drives for an offline image that has been prepared with the Sysprep tool. Note that the wizard does not have the ability to capture a partial volume.

  5. The Image Capture Wizard extracts metadata from data points in the offline image (such as the hardware abstraction layer (HAL) type, architecture, product name and type, operating system version, and language).

  6. The Image Capture Wizard captures the selected volume and saves it to the specified .wim file.

  7. The Image Capture Wizard updates the metadata of the image with the information that was extracted from the offline image, in addition to any values that were input by the user.

  8. The Image Capture Wizard uploads the image to the Windows Deployment Services server (optional).