| # Blobfs: A content-addressable filesystem for Fuchsia |
| |
| 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](/docs/concepts/filesystems/minfs.md) handles this case). |
| |
| The structure of blobfs is described in the [main |
| documentation](/docs/concepts/filesystems/blobfs.md). This page documents some internal details. |
| |
| ## Version notes |
| |
| Blobfs follows the [storage versioning scheme](/src/storage/docs/versioning.md). 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: |
| |
| * 8.1, 9.1: The initial minor version. |
| * 8.2, 9.2: Introduced a backup superblock when running under FVM. |
| * 8.3, 9.3: Removed support for ZSTD seekable compression. |
