Blobfs is a filesystem for Fuchsia that stores all files according to their hashes. This is used for all binaries and other program-related data for Fuchsia. It is not used for storing dynamic data and it has no hierarchy (minfs handles this case).
The structure of blobfs is described in the main documentation. This page documents some internal details.
Blobfs follows the storage versioning scheme. However, there were some versions before this was adopted that do not follow this scheme.
In major version 8, blobfs used “padded” Merkle trees. In this format, the Merkle tree was padded out to the nearest block boundary and immediately preceeded the blob data on the block device.
In major version 9, blobfs switched to “compact” Merkle trees where the Merkle tree data immediately follows the blob data and neither the offset nor the size is block-padded. This saves space. This change was made when the minor version was treated as a monotonically increasing “revision” and was not reset. As of this writing the format is controlled by a build flag so some builds will have major version 8, while others will have major version 9.
Across versions 8 and 9 are the following minor versions: