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Date: Fri, 17 Jun 2016 09:25:24 -0600
From: Andreas Dilger <adilger@...ger.ca>
To: Lars Wijtemans <lars@...temans.nl>
Cc: linux-ext4@...r.kernel.org
Subject: Re: PROBLEM: incorrect data block bitmap after running resize2fs and e2fsck
Ted has just released 1.43.1 that fixes a number of problems with 1.42.13.
You might also consider trying 1.42.13 if you haven't enabled any of the new features in 1.43 (data checksums, inline data, etc.).
Cheers, Andreas
> On Jun 17, 2016, at 08:55, Lars Wijtemans <lars@...temans.nl> wrote:
>
> After shrinking an ext4 filesystem with resize2fs and running e2fsck
> afterwards, total free blocks count is wrong. Blocks which are "not in
> use" according to debugfs are in fact found to be used by the icheck
> command of debugfs. Subsequent runs of e2fsck report no problems with
> this filesystem.
>
>
> == System information
> Linux 4.5.6-200.fc23.x86_64
> e2fsprogs 1.42.13 (17-May-2015)
>
>
> == What led to the problem
> I wanted to shrink an ext4 filesystem. The filesystem was created a
> while ago (probably with the -E resize=xyz option) and has been resized
> before.
> It is layered like this: GPT partition | RAID | LUKS | LVM | ext4
>
> (21694432 MiB total size at this point)
>
> # e2fsck -f /dev/mapper/foo
> No filesystem problems were found.
>
> # resize2fs -P /dev/mapper/foo
> (20248275 MiB)
>
> # resize2fs /dev/mapper/foo 21693408M
> # e2fsck -nf /dev/mapper/foo
> (No filesystem problems were found)
>
> # resize2fs -p /dev/mapper/foo 21170144M
> # resize2fs -p /dev/mapper/foo 20645856M
> # e2fsck -nf /dev/mapper/foo
> There were a lot of "Free blocks count wrong" wrong messages. Some
> searching on the internet let me to believe this was to be expected, so
> I re-ran with the "preen" option.
>
> # e2fsck -fp /dev/mapper/foo
> (This completed without any meaningful output)
>
> The filesystem contained about 19 TiB of data. After mounting, df
> showed only 13 TiB in use. I immediately re-mounted in read-only mode.
> Walking the filesystem still shows a total 19.2 TiB of data that seems
> to be uncorrupted (check ongoing).
> Subsequent runs of e2fsck do not find any problems.
>
>
> == Going from here...
> I am concerned that writing to this filesystem will result in data
> loss, since a lot of blocks are (incorrectly) marked as free. It also
> seems like something e2fsck should be able to fix, since the files are
> accessible without problems in read-only mode. I can even imagine
> fixing this through debugfs, by checking whether a block is used by a
> file and, if so, mark it as such.
>
> What I would like to do is
> 1) figure out why e2fsck is not able to detect/fix this by itself,
> hopefully resulting in an improvement in e2fsck and
> 2) (manually) restore the filesystem to a usable state (within about
> two weeks).
>
> I'm not familiar with ext4 internals, so any help here is appreciated.
>
>
> # df --block-size=4096 /data
> Filesystem 4K-blocks Used Available Use%
> /dev/mapper/vg_datagroup-bulk 5282123045 3385286984 1666833796 68%
>
> # du --block-size=4096 --summarize --one-file-system /data
>
>
> # debugfs /dev/mapper/foo -R "testb 1 5285339135" > /tmp/testb.txt
> Block 1 marked in use
> [...]
> Block 32768 not in use
> [...]
>
> # grep " not in use" /tmp/testb.txt | wc -l
> 1896836061
>
> # grep " marked in use" /tmp/testb.txt | wc -l
> 3388503074
>
> # grep " not in use" /tmp/testb.txt | shuf -n 100 | \
> awk '{print $2}' | tr '\n' " "
> 265503904 1397137951 924616805 [...]
>
> These blocks should not have any files associated with them.
>
> # debugfs /dev/mapper/foo -R "icheck 265503904 1397137951 [...]"
> debugfs 1.42.13 (17-May-2015)
> Block Inode number
> 265503904 9569537
> 1397137951 8697
> 924616805 4764587
> 920525308 11513483
> 4032323069 <block not found>
> 814305093 1539116
> 246137426 26227968
> 456159649 21
> 277352417 2861448
> [...]
>
>
> # dumpe2fs -h /dev/mapper/foo
> dumpe2fs 1.42.13 (17-May-2015)
> Filesystem volume name: bulk
> Last mounted on: /data
> Filesystem UUID: dc0f67cf-85a4-421f-8387-0fb2de7f03ff
> Filesystem magic number: 0xEF53
> Filesystem revision #: 1 (dynamic)
> Filesystem features: has_journal ext_attr dir_index filetype
> meta_bg extent 64bit flex_bg sparse_super large_file huge_file
> uninit_bg dir_nlink extra_isize
> Filesystem flags: signed_directory_hash
> Default mount options: user_xattr acl
> Filesystem state: clean
> Errors behavior: Remount read-only
> Filesystem OS type: Linux
> Inode count: 41291776
> Block count: 5285339136
> Reserved block count: 229998169
> Free blocks: 1896836061
> Free inodes: 9341404
> First block: 0
> Block size: 4096
> Fragment size: 4096
> Group descriptor size: 64
> Blocks per group: 32768
> Fragments per group: 32768
> Inodes per group: 256
> Inode blocks per group: 16
> RAID stride: 128
> RAID stripe width: 768
> First meta block group: 1956
> Flex block group size: 4096
> Filesystem created: Sun Sep 7 13:05:00 2014
> Last mount time: Thu Jun 16 10:38:57 2016
> Last write time: Thu Jun 16 10:39:41 2016
> Mount count: 1
> Maximum mount count: 20
> Last checked: Thu Jun 16 09:55:23 2016
> Check interval: 1382400 (2 weeks, 2 days)
> Next check after: Sat Jul 2 09:55:23 2016
> Lifetime writes: 44 TB
> Reserved blocks uid: 0 (user root)
> Reserved blocks gid: 0 (group root)
> First inode: 11
> Inode size: 256
> Required extra isize: 28
> Desired extra isize: 28
> Journal inode: 8
> Default directory hash: half_md4
> Directory Hash Seed: 656e1be4-f041-41c8-a3e8-63827db144bd
> Journal backup: inode blocks
> Journal features: journal_incompat_revoke journal_64bit
> Journal size: 1024M
> Journal length: 262144
> Journal sequence: 0x00192c59
> Journal start: 0
> Bad blocks: 2639100416, 2639100417, [...]
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