btrfs-rescue man page
btrfs-rescue — Recover a damaged btrfs filesystem
btrfs rescue <subcommand> <args>
btrfs rescue is used to try to recover a damaged btrfs filesystem.
chunk-recover [options] <device>
Recover the chunk tree by scanning the devices
Since chunk-recover will scan the whole device, it will be VERY slow especially executed on a large device.
super-recover [options] <device>
Recover bad superblocks from good copies.
clear the filesystem log tree
This command will clear the filesystem log tree. This may fix a specific set of problem when the filesystem mount fails due to the log replay. See below for sample stacktraces that may show up in system log.
The common case where this happens has been fixed a long time ago, so it is unlikely that you will see this particular problem, but the utility is kept around.
clearing the log may lead to loss of changes that were made since the last transaction commit. This may be up to 30 seconds (default commit period) or less if the commit was implied by other filesystem activity.
One can determine whether zero-log is needed according to the kernel backtrace:
? replay_one_dir_item+0xb5/0xb5 [btrfs] ? walk_log_tree+0x9c/0x19d [btrfs] ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs] ? btrfs_recover_log_trees+0x195/0x29c [btrfs] ? replay_one_dir_item+0xb5/0xb5 [btrfs] ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs] ? open_ctree+0xff6/0x132c [btrfs]
If the errors are like above, then zero-log should be used to clear the log and the filesystem may be mounted normally again. The keywords to look for are open_ctree which says that it’s during mount and function names that contain replay, recover or log_tree.
btrfs rescue returns a zero exit status if it succeeds. Non zero is returned in case of failure.
btrfs is part of btrfs-progs. Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for further details.
mkfs.btrfs(8), btrfs-scrub(8), btrfs-check(8)
btrfs(8), btrfs-check(8), btrfs-restore(8).