Choosing a Data Store Location

USMT stores user state in a data store. USMT can create the data store in a variety of locations and media during migration. By default, USMT creates a store file that contains compressed user data. It can also encrypt the data store to protect the data during the transition to the new operating system. As you prepare for user state migration, you must determine the best location for the USMT data store.

Consider the following when locating the USMT data store:

• Hard-link migration reduces storage requirements During a hard-link migration, USMT maps how a collection of bits on the hard disk is wired into the file system. It allows you to remove the old operating system and install Windows 7 without requiring you to create copies of the original files. After installing Windows 7, USMT restores the original file links. Hard-link migration uses significantly less disk space and takes considerably less time, but you can perform a hard-link migration only in the Refresh Computer scenario.
• USMT cannot store multiple operations in the same file USMT operations can collect data from more than one user but cannot store more than one operation in a single store file. In a high-volume migration, you can either locate the data store locally (which is only possible because the Windows 7 imaging process is nondestructive) or locate each data store on the network (possibly organized by computer name). Note that MDT 2010 handles the data store location automatically and provides choices for customizing it.
• User state data can use significant space When creating your migration plan, you can run the ScanState component of USMT with the /p:<path to a file> command-line option to create a size estimate. If you're locating the data store on a server, rather than locally, run this command on a representative sample of computers in the environment to calculate the storage required.
• The USMT data store must be accessible to both the source and target systems When writing to or reading from the data store, USMT must have access to that data store. Locate the file somewhere that will be available to both computers. MDT 2010 handles this issue somewhat transparently. If you're locating the data store locally, access is not an issue.

Local Data Stores

You can locate the USMT data store on the local disk in the Refresh Computer scenario. ImageX and Windows Setup are nondestructive, which means that they can install the operating system without destroying the data on the disk. This optimizes the speed of the migration process because network speeds and removable media speeds are factored out of the process. MDT 2010 provides the option to use local data stores.

A better option is using a hard-link migration store, which enables you to perform an in-place migration in which USMT maintains all user state on the local computer while you remove the old operating system and install the new operating system. Therefore, hard-link migration is suitable only for the Refresh Computer scenario. Using a hard-link migration store drastically improves migration performance and significantly reduces hard-disk utilization, reduces deployment costs, and enables entirely new migration scenarios.

Remote Data Stores

In the Replace Computer (side-by-side) and New Computer scenarios, you can put the USMT data store on a network server. In these scenarios, putting the data store on the network is necessary because the local data store will not be available in the postinstallation phase.

Removable Storage

You can also put USMT store files on removable media during the migration process. You can use flash disks and portable hard disks to simplify this process. Because this step adds interaction to the process, it is recommended only in bench deployments or in scenarios in which you've already factored interaction into the deployment process.