For any one who wants to try it, it can be get from my repo:
https://github.com/adam900710/btrfs-progs/tree/offline_scrub
Several reports on kernel scrub screwing up good data stripes are in ML
for sometime.
And since kernel scrub won't account P/Q corruption, it makes us quite
hard to detect error like kernel screwing up P/Q when scrubbing.
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 patchset 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 should be finally replaced by
offline scrub.
As "--check-data-csum" doesn't really check all mirrors, if it hits
a good copy, then resting copies will just be ignored.
In v4 update, data check is further improved, inspired by kernel
behavior, now data extent is checked sector by sector, so it can
handle the following corruption case:
Data extent A contains data from 0~28K.
And |///| = corrupted | | = good
0 4k 8k 12k 16k 20k 24k 28k
Mirror 0 |///| |///| |///| | |
Mirror 1 | |///| |///| |///| |
Extent A should be RECOVERABLE, while in v3 we treat data extent A as
a whole unit, above case is reported as CORRUPTED.
2) RAID5/6 full stripe check
It will take full use of btrfs csum(both tree and data).
It will only recover the full stripe if all recovered data matches
with its csum.
NOTE: Due to the lack of good bitmap facilities, RAID56 sector by
sector repair will be quite complex, especially when NODATASUM is
involved.
So current RAID56 doesn't support vertical sector recovery yet.
Data extent A contains data from 0~64K
And |///| = corrupted while | | = good
0 8K 16K 24K 32K 40K 48K 56K 64K
Data stripe 0 |///| |///| |///| |///| |
Data stripe 1 | |///| |///| |///| |///|
Parity | | | | | | | | |
Kernel will recover it, while current scrub will report it as
CORRUPTED.
3) Repair
In this v4 update, repair is finally added.
And this patchset also introduces new btrfs_map_block() function, which is
more flex than current btrfs_map_block(), and has a unified interface
for all profiles, not just an extra array for RAID56.
Check the 6th and 7th patch for details.
They are already used in RAID5/6 scrub, but can also be used for other
profiles too.
The to-do list has been shortened, since repair is added in v4 update.
1) Test cases
Need to make the infrastructure able to handle multi-device first.
2) Make btrfsck able to handle RAID5 with missing device
Now it doesn't even open RAID5 btrfs with missing device, even though
scrub should be able to handle it.
3) RAID56 vertical sector repair
Although I consider such case is minor compared to RAID1 vertical
sector repair.
As for RAID1, an extent can be as large as 128M, while for RAID56 one
stripe will always be 64K, much smaller than RAID1 case, making the
possibility lower.
I prefer to add this function after the patchset get merged, as no
one really likes get 20 mails every time I update the patchset.
For guys who want to review the patchset, there is a basic function
relationships slide.
I hope this will reduce the time needed to get what the patchset is
doing.
https://docs.google.com/presentation/d/1tAU3lUVaRUXooSjhFaDUeyW3wauHDSg9H-AiLBOSuIM/edit?usp=sharing
Qu Wenruo (20):
btrfs-progs: raid56: Introduce raid56 header for later recovery usage
btrfs-progs: raid56: Introduce tables for RAID6 recovery
btrfs-progs: raid56: Allow raid6 to recover 2 data stripes
btrfs-progs: raid56: Allow raid6 to recover data and p
btrfs-progs: Introduce wrapper to recover raid56 data
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: csum: Introduce function to read out data csums
btrfs-progs: scrub: Introduce structures to support offline scrub for
RAID56
btrfs-progs: scrub: Introduce functions to scrub mirror based tree
block
btrfs-progs: scrub: Introduce functions to scrub mirror based data
blocks
btrfs-progs: scrub: Introduce function to scrub one mirror-based
extent
btrfs-progs: scrub: Introduce function to scrub one data stripe
btrfs-progs: scrub: Introduce function to verify parities
btrfs-progs: extent-tree: Introduce function to check if there is any
extent in given range.
btrfs-progs: scrub: Introduce function to recover data parity
btrfs-progs: scrub: Introduce helper to write a full stripe
btrfs-progs: scrub: Introduce a function to scrub one full stripe
btrfs-progs: scrub: Introduce function to check a whole block group
btrfs-progs: scrub: Introduce offline scrub function
.gitignore | 2 +
Documentation/btrfs-scrub.asciidoc | 9 +
Makefile | 19 +-
cmds-scrub.c | 116 ++-
csum.c | 136 ++++
ctree.h | 12 +
disk-io.c | 4 +-
disk-io.h | 6 +-
extent-tree.c | 60 ++
kerncompat.h | 3 +
kernel-lib/mktables.c | 148 ++++
kernel-lib/raid56.c | 359 ++++++++++
kernel-lib/raid56.h | 58 ++
raid56.c | 172 -----
scrub.c | 1370 ++++++++++++++++++++++++++++++++++++
utils.h | 12 +
volumes.c | 283 ++++++++
volumes.h | 78 ++
18 files changed, 2660 insertions(+), 187 deletions(-)
create mode 100644 csum.c
create mode 100644 kernel-lib/mktables.c
create mode 100644 kernel-lib/raid56.c
create mode 100644 kernel-lib/raid56.h
delete mode 100644 raid56.c
create mode 100644 scrub.c
--
2.13.0
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