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USMT 4.0 Temporary and Working Space Explanations

  • Article

The User State Migration Tool uses temporary files and working space during a migration with scanstate. This article seeks to explain some of the more common questions around the architecture of this usage in order to better estimate free space requirements.

Explanation

By default, the USMT temp/working folder is the operator's %TEMP% folder (this is always local to the computer). The full set of files is not gathered here; the store is updated in a serialized fashion directly. The temporary file that USMT 4.0 creates is used purely to track work and back the stores catalog data and non-file data.

When running scanstate.exe /p the estimator for space figures how big the backing file will get, then adds an additional 1MB of "fudge factor". The binary size of gathered user data files never matters -just the quantity of units to be migrated.

For example, consider a Windows 7 client with eight user profiles. This created a temporary backing file that was 44MB. When the migration was limited to a single user profile the temporary file was only 9MB. When 300MB of data was added to that profile (only 20 files, but each being very large), the temporary space usage estimate did not increase appreciably:

<?xml version="1.0" encoding="UTF-8"?>
<PreMigration>
<storeSize>
<size clusterSize="4096">96075776</size>
</storeSize>
<temporarySpace>
<size>10576664</size>
</temporarySpace>
</PreMigration>

<?xml version="1.0" encoding="UTF-8"?>
<PreMigration>
<storeSize>
<size clusterSize="4096">425594880</size>
</storeSize>
<temporarySpace>
<size>10617624</size>
</temporarySpace>
</PreMigration>

Estimating Migration Store Size

  • Scanstate and loadstate automatically require at least 250MB free hard drive space and will exit fatally otherwise. This check cannot be overridden, decreased, or increased - it is hard-coded. Failure to detect that much free space returns error:

Failed
   A minimum of 250 MB of free space is required for temporary files

Scanstate return code: 29

  • Additional temporary drive space is required for non-hardlink migrations, as copies of the files are made that are then added to the store. This does not include the aforementioned 250MB free space (which is mainly set aside for pagefile growth). Scanstate.exe /p will estimate this amount of space with decent accuracy.