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Fast Virtual Disk (FVD) is a new QEMU image format developed at IBM Research (see the FVD web site). FVD was designed for both high performance and flexibility, and it indeed achieves both goals. As a next-generation image format, FVD surpasses existing image formats in two simple but fundamental ways:

  • FVD separates the functions of copy-on-write and storage allocation so that storage allocation can be performed by any component, i.e., a component that is most appropriate for a given scenario, be it a host file system, a host logical volume manager, FVD itself, or even another image format. This is the key in achieving high performance.
  • FVD treats image mobility as a first-class citizen, and provides copy-on-read and adaptive prefetching of base image, in addition to the widely used copy-on-write technique.


FVD (a.k.a ODS) was operational since June 2010. Now the implementation is mature and patches have been submitted for consideration of adoption in the QEMU main line. See the archive.


Read Why FVD.

How FVD Works

Read How FVD Works.

Rigorous Engineering of FVD

Read Rigorous Engineering of FVD.

Detailed Specification of FVD

Read the FVD Specification.

Comparing FVD and QED

Read Comparing FVD and QED.