***Just RFC patch for early evaluation, please don't merge it*** For any one who wants to try it, it can be get from my repo: https://github.com/adam900710/btrfs-progs/tree/fsck_scrub
Currently, I only tested it on SINGLE/DUP/RAID1/RAID5 filesystems, with mirror or parity or data corrupted. The tool are all able to detect them and give recoverbility report. Several reports on kernel scrub screwing up good data stripes are in ML for sometime. The reason seems to be lack of csum check before and after reconstruction, and unfinished parity write seems also involved. To get a comparable tool for kernel scrub, we need a user-space tool to act as benchmark to compare their different behaviors. So here is the RFC patch set for user-space scrub. Which can do: 1) All mirror/backup check for non-parity based stripe Which means for RAID1/DUP/RAID10, we can really check all mirrors other than the 1st good mirror. Current "--check-data-csum" option will be finally replace by scrub. As it doesn't really check all mirrors, if it hits a good copy, then resting copies will just be ignored. 2) Comprehensive RAID5 full stripe check It will check csum before reconstruction using parity. And if too many data stripes has csum mismatch, no need to reconstruct anyway. And after reconstruction, it will also check the csum of recovered data against csum, to ensure we didn't recover wrong result. For all csum match case, will re-calculate parity and compare it with ondisk parity, to detect parity error. In fact, it can already expose one new btrfs kernel bug. For example, after screwing up a data stripe, kernel did repairs using parity, but recovered full stripe has wrong parity. Need to scrub again to fix it. And this patchset also introduced new map_block() function, which is more flex than current btrfs_map_block(), and has a unified interface for all profiles. Check the 1st and 2nd patch for details. They are already used in RAID5/6 scrub, but can also be used for other profiles too. Since it's just an evaluation patchset, it still has a long to-do list: 1) Repair support In fact, current tool can already report recoverability, repair is not hard to implement. 2) RAID6 support The mathematics behind RAID6 recover is more complex than RAID5. Need some more code to make it possible to recover data stripes, other than just calculating Q and P. 3) Test cases Need to make the infrastructure able to handle multi-device first. 4) Cleaner code and refined logical Need a better shared logical for all profiles to do scrub, and use new map_block_v2() to replace these old codes. 5) Make btrfsck able to handle RAID5 with missing device Now it doesn't even open RAID5 btrfs with missing device, even thouth scrub should be able to handle it. Qu Wenruo (14): btrfs-progs: Introduce new btrfs_map_block function which returns more unified result. btrfs-progs: Allow __btrfs_map_block_v2 to remove unrelated stripes btrfs-progs: check/csum: Introduce function to read out one data csum btrfs-progs: check/scrub: Introduce structures to support fsck scrub btrfs-progs: check/scrub: Introduce function to scrub mirror based tree block btrfs-progs: check/scrub: Introduce function to scrub mirror based data blocks btrfs-progs: check/scrub: Introduce function to scrub one extent btrfs-progs: check/scrub: Introduce function to scrub one data stripe btrfs-progs: check/scrub: Introduce function to verify parities btrfs-progs: extent-tree: Introduce function to check if there is any extent in given range. btrfs-progs: check/scrub: Introduce function to recover data parity btrfs-progs: check/scrub: Introduce a function to scrub one full stripe btrfs-progs: check/scrub: Introduce function to check a whole block group btrfs-progs: fsck: Introduce offline scrub function Documentation/btrfs-check.asciidoc | 8 + Makefile.in | 6 +- check/check.h | 23 ++ check/csum.c | 96 +++++ check/scrub.c | 812 +++++++++++++++++++++++++++++++++++++ cmds-check.c | 12 +- ctree.h | 2 + disk-io.c | 4 +- disk-io.h | 2 + extent-tree.c | 52 +++ volumes.c | 282 +++++++++++++ volumes.h | 49 +++ 12 files changed, 1343 insertions(+), 5 deletions(-) create mode 100644 check/check.h create mode 100644 check/csum.c create mode 100644 check/scrub.c -- 2.10.0 -- To unsubscribe from this list: send the line "unsubscribe linux-btrfs" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html