6 btrfs-rescue - Recover a damaged btrfs filesystem
10 *btrfs rescue* <subcommand> <args>
14 *btrfs rescue* is used to try to recover a damaged btrfs filesystem.
18 *chunk-recover* [options] <device>::
19 Recover the chunk tree by scanning the devices
24 assume an answer of 'yes' to all questions.
30 NOTE: Since *chunk-recover* will scan the whole device, it will be *VERY* slow
31 especially executed on a large device.
33 *super-recover* [options] <device>::
34 Recover bad superblocks from good copies.
39 assume an answer of 'yes' to all questions.
44 clear the filesystem log tree
46 This command will clear the filesystem log tree. This may fix a specific
47 set of problem when the filesystem mount fails due to the log replay. See below
48 for sample stacktraces that may show up in system log.
50 The common case where this happens has been fixed a long time ago,
51 so it is unlikely that you will see this particular problem, but the utility is
54 NOTE: clearing the log may lead to loss of changes that were made since the
55 last transaction commit. This may be up to 30 seconds (default commit period)
56 or less if the commit was implied by other filesystem activity.
58 One can determine whether *zero-log* is needed according to the kernel
62 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
63 ? walk_log_tree+0x9c/0x19d [btrfs]
64 ? btrfs_read_fs_root_no_radix+0x169/0x1a1 [btrfs]
65 ? btrfs_recover_log_trees+0x195/0x29c [btrfs]
66 ? replay_one_dir_item+0xb5/0xb5 [btrfs]
67 ? btree_read_extent_buffer_pages+0x76/0xbc [btrfs]
68 ? open_ctree+0xff6/0x132c [btrfs]
71 If the errors are like above, then *zero-log* should be used to clear
72 the log and the filesystem may be mounted normally again. The keywords to look
73 for are 'open_ctree' which says that it's during mount and function names
74 that contain 'replay', 'recover' or 'log_tree'.
76 *fix-device-size* <device>::
77 fix device size and super block total bytes
79 This command will fix the following problems, by re-aligning all devices' total
80 bytes and re-calculating super block total bytes.
82 1. Newer kernel refuse to mount btrfs caused by mismatch super block total bytes
85 BTRFS error (device sdb): super_total_bytes 92017859088384 mismatch with fs_devices total_rw_bytes 92017859094528
88 2. Noisy kernel warning for newer kernels
91 WARNING: CPU: 3 PID: 439 at fs/btrfs/ctree.h:1559 btrfs_update_device+0x1c5/0x1d0 [btrfs]
94 And the corresponding line is the `WARN_ON()` line below:
98 BUILD_BUG_ON(sizeof(u64) !=
99 sizeof(((struct btrfs_dev_item *)0))->total_bytes);
100 WARN_ON(!IS_ALIGNED(val, eb->fs_info->sectorsize));
101 btrfs_set_64(eb, s, offsetof(struct btrfs_dev_item, total_bytes), val);
107 *btrfs rescue* returns a zero exit status if it succeeds. Non zero is
108 returned in case of failure.
112 *btrfs* is part of btrfs-progs.
113 Please refer to the btrfs wiki http://btrfs.wiki.kernel.org for