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Diffstat (limited to 'fs/btrfs/dev-replace.c')
| -rw-r--r-- | fs/btrfs/dev-replace.c | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/fs/btrfs/dev-replace.c b/fs/btrfs/dev-replace.c index 2ca2a09d0e23..2aad07cdaea8 100644 --- a/fs/btrfs/dev-replace.c +++ b/fs/btrfs/dev-replace.c @@ -22,6 +22,46 @@ #include "dev-replace.h" #include "sysfs.h" +/* + * Device replace overview + * + * [Objective] + * To copy all extents (both new and on-disk) from source device to target + * device, while still keeping the filesystem read-write. + * + * [Method] + * There are two main methods involved: + * + * - Write duplication + * + * All new writes will be written to both target and source devices, so even + * if replace gets canceled, sources device still contans up-to-date data. + * + * Location: handle_ops_on_dev_replace() from __btrfs_map_block() + * Start: btrfs_dev_replace_start() + * End: btrfs_dev_replace_finishing() + * Content: Latest data/metadata + * + * - Copy existing extents + * + * This happens by re-using scrub facility, as scrub also iterates through + * existing extents from commit root. + * + * Location: scrub_write_block_to_dev_replace() from + * scrub_block_complete() + * Content: Data/meta from commit root. + * + * Due to the content difference, we need to avoid nocow write when dev-replace + * is happening. This is done by marking the block group read-only and waiting + * for NOCOW writes. + * + * After replace is done, the finishing part is done by swapping the target and + * source devices. + * + * Location: btrfs_dev_replace_update_device_in_mapping_tree() from + * btrfs_dev_replace_finishing() + */ + static int btrfs_dev_replace_finishing(struct btrfs_fs_info *fs_info, int scrub_ret); static void btrfs_dev_replace_update_device_in_mapping_tree( |