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Win10 Full Flash Update

Since Version 1607, Windows Server has included support for an image format named FFU. Short for Full Flash Update, this format lays down a runtime image on a physical drive. FFU support comes to Windows 10 as of Version 1709. It can create runnable Windows and recovery images, and a complete system partition scheme in one go. Designed for speed (it proves itself fast in practice) and supports larger files than Windows Image format (aka WIM). This is fully documented at Microsoft’s Hardware Dev Center where two articles specifically target FFU. The first is Windows Full Flash Update (FFU) images, the second WIM vs. VHD vs. FFU: comparing image file formats. Win10 Full Flash Update offers some nice advantages, which I will recite shortly.

Digging into Win10 Full Flash Update

A quick visit to the second cited article above reveals FFU’s key characteristics. It is the fastest tool for capturing and deploying Windows on the factory floor (it’s aimed at OEMs). It is sector-based and uses the highly compact Xpress-Huffman compression algorithm. FFU captures a complete set of drive information including partition data. When FFUtool is used to apply an image, it starts by cleaning the entire drive. When deploying from a source image, the target drive must be the same size as the original (source) drive, or larger. DISM works with FFU images, so they may be mounted for manipulation, then modified, then dismounted to deploy updates and changes. FFU also includes a catalog and hash table to validate signatures upfront before flashing gets underway. A hash table is generated during the capture process, then validated when the image gets applied (neither WIM nor VHD support this added reliability check).

You can use FFU with Windows 10 right now through the Deployment Image Servicing and Management (DISM) command-line utility. Recent ad-hoc tests using DISM and WIM versus DISM and FFU shows off FFU’s speed advantage. On a pair of test technician machines, the speed difference was better than 50% for each one when comparing the time it takes to apply a WIM image as compared to its FFU counterpart (same OS, same modifications, same everything). FFU is good stuff, and worth getting to know for those in the image deployment game.

See the FFU image format article at the MS Hardware Dev Center for depictions of FFU V1 and V2 disk layout schemes. The second version supports multiple data stores so it can accommodate multiple, unrelated images in a single file.

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