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authorNaohiro Aota <naohiro.aota@wdc.com>2021-02-04 13:22:16 +0300
committerDavid Sterba <dsterba@suse.com>2021-02-09 04:46:07 +0300
commitf7ef5287a63d644e62a52893af8c6cfcb5043213 (patch)
treef9c168ecddce9d6c539e56533497b2be3eab1ba1 /fs/Makefile
parent32430c614844169a5e5554dcbb307735ddd1f780 (diff)
downloadlinux-f7ef5287a63d644e62a52893af8c6cfcb5043213.tar.xz
btrfs: zoned: relocate block group to repair IO failure in zoned filesystems
When a bad checksum is found and if the filesystem has a mirror of the damaged data, we read the correct data from the mirror and writes it to damaged blocks. This however, violates the sequential write constraints of a zoned block device. We can consider three methods to repair an IO failure in zoned filesystems: (1) Reset and rewrite the damaged zone (2) Allocate new device extent and replace the damaged device extent to the new extent (3) Relocate the corresponding block group Method (1) is most similar to a behavior done with regular devices. However, it also wipes non-damaged data in the same device extent, and so it unnecessary degrades non-damaged data. Method (2) is much like device replacing but done in the same device. It is safe because it keeps the device extent until the replacing finish. However, extending device replacing is non-trivial. It assumes "src_dev->physical == dst_dev->physical". Also, the extent mapping replacing function should be extended to support replacing device extent position in one device. Method (3) invokes relocation of the damaged block group and is straightforward to implement. It relocates all the mirrored device extents, so it potentially is a more costly operation than method (1) or (2). But it relocates only used extents which reduce the total IO size. Let's apply method (3) for now. In the future, we can extend device-replace and apply method (2). For protecting a block group gets relocated multiple time with multiple IO errors, this commit introduces "relocating_repair" bit to show it's now relocating to repair IO failures. Also it uses a new kthread "btrfs-relocating-repair", not to block IO path with relocating process. This commit also supports repairing in the scrub process. Reviewed-by: Josef Bacik <josef@toxicpanda.com> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com> Signed-off-by: David Sterba <dsterba@suse.com>
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