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Overlayfs snapshots
Overlayfs snapshots project is discontinued.
Please visit the project page for the successor overlayfs watch project.
Overlayfs snapshots adds file level snapshots capability to any local file system.
- Incremental read-only snapshots of directory sub-tree
- Independent of underlying local file system
- Inode cache of unmodified files is shared among all snapshots
- Snapshots use available file system disk space
- Snapshot deletion automatically frees up disk space
- Minimal performance overhead to file system operation in the writable mount
- POSIX compliance for file system operation in the writable mount
- File access to read-only snapshots may be slower then local file system access
- Reading from snapshots may exhibit some overlayfs non-standard behavior
- Take new snapshot in O(1) time and disk space
- No upper limit on number or size of snapshots
Slides for Vault Conference 2017 (PDF format)
The latest overlayfs snapshot patches are available on ovl_snapshot branch on github.
Overlayfs snapshots are regularly tested over underlying file system xfs formatted with reflink support, which provides adequate file copy up performance.
The unionmount test suite was originally developed by David Howells to test for union file system correctness. The test suite was enhanced to be able to setup overlayfs over xfs+reflink and instrumented with overlayfs snapshot consistency validation tests.
Visit the Snapshots testing page for instructions how to run these tests.
POSIX compliance tests and general VFS system calls coverage are run on regular basis both on overlayfs mount and snapshot mount using the pjdfstest test suite.
Tests to track specific overlayfs issues are being developed for xfstests. The xfstests-bld KVM image is used to run xfstests and it was enhanced to be able to run the overlayfs over xfs+reflink configuration.
Known overlayfs snapshots POC issues are tracked on github.
Contributions to overlayfs snapshots project are most welcome in the form of code review, testing, articles and public attention.
Please post any questions to the author of the patches and CC [email protected]. Please subscribe to linux-unionfs to get updates on the project.