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GitHub Introduce zfs rewrite subcommand
master ← amotin:rewrite
opened 08:33PM - 15 Apr 25 UTC
### Motivation and Context
For years users were asking for an ability to re-bal… ance pool after vdev addition, de-fragment randomly written files, change some properties for already written files, etc. The closest option would be to either copy and rename a file or send/receive/rename the dataset. Unfortunately all of those options have some downsides.
### Description
This change introduces new `zfs rewrite` subcommand, that allows to rewrite content of specified file(s) as-is without modifications, but at a different location, compression, checksum, dedup, copies and other parameter values. It is faster than read plus write, since it does not require data copying to user-space. It is also faster for sync=always datasets, since without data modification it does not require ZIL writing. Also since it is protected by normal range range locks, it can be done under any other load. Also it does not affect file's modification time or other properties.
### How Has This Been Tested?
Manually tested it on FreeBSD. Linux-specific code is not yet tested.
### Types of changes
- [ ] Bug fix (non-breaking change which fixes an issue)
- [x] New feature (non-breaking change which adds functionality)
- [ ] Performance enhancement (non-breaking change which improves efficiency)
- [ ] Code cleanup (non-breaking change which makes code smaller or more readable)
- [ ] Breaking change (fix or feature that would cause existing functionality to change)
- [ ] Library ABI change (libzfs, libzfs\_core, libnvpair, libuutil and libzfsbootenv)
- [ ] Documentation (a change to man pages or other documentation)
### Checklist:
- [x] My code follows the OpenZFS [code style requirements](https://github.com/openzfs/zfs/blob/master/.github/CONTRIBUTING.md#coding-conventions).
- [ ] I have updated the documentation accordingly.
- [ ] I have read the [**contributing** document](https://github.com/openzfs/zfs/blob/master/.github/CONTRIBUTING.md).
- [ ] I have added [tests](https://github.com/openzfs/zfs/tree/master/tests) to cover my changes.
- [ ] I have run the ZFS Test Suite with this change applied.
- [x] All commit messages are properly formatted and contain [`Signed-off-by`](https://github.com/openzfs/zfs/blob/master/.github/CONTRIBUTING.md#signed-off-by).
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00:00 ZFS Rewrite Explained
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