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Determining Image Size in Standard 7 (2011) - Part 2

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In part 1, I discussed how we produced our footprint estimates for eCore and other packages. There are many variables to consider when measuring footprint, and when determining actual footprint requirements for an actual device, an actual measurement will produce the most accurate measurement. This is particularly important for devices with limited storage capabilities.

When developing a runtime, it’s important to use a volume size that matches your intended device’s storage capability (i.e. don’t use a 40 GB partition on your development machine, when your device will only have a 4 GB partition). This is because NTFS itself creates a map of the volume and stores it in metadata. The size of this map varies based on volume size. For example, an empty 1 GB NTFS partition uses 33 MB of metadata to store this map.

The ideal way to measure actual footprint is to deploy the actual image onto a test device with the actual intended partition size. To calculate actual footprint, use data from the fsutil.exe tool:

  • Fsutil fsinfo ntfsinfo <volume>

From the console output:

  • subtract free clusters from total clusters
  • Convert value to decimal, and multiply by the bytes per cluster
  • The result is the space needed in bytes

Some variables to consider when considering image size:

  • Volume size – larger volumes consume more metadata, but as volumes get larger, this becomes trivial
  • Additional drivers needed by the device – in addition to the actual file size, additional disk space is required for the ACLs.
  • Actual Language pack(s) and required font(s) that are selected
  • Application needs – some applications require additional storage to function. For example Internet Explorer 8 requires additional space for the history, cookies and plug-ins. Ready Boost creates cache files, etc.
  • Future servicing updates
  • Additional Applications
  • User generated data

Footprint estimates in Windows Embedded Standard 7 (formerly known as Standard 2011) can vary from actual footprint for reasons as described above. If disk space is critical, the best thing is to measure the actual image size.

- Tony

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