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Olaf Mandel
Asked: 2020-06-09 06:23:34 +0800 CST

Reason for EXT4 file system corruption of Hyper-V guest

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We had our second corruption of an ext4 partition in a relatively short time and ext4 is supposedly very reliable. As this is a virtual machine and the host providing the resources saw no disk errors or power-loss or such, I want to rule out hardware errors for now.

So I am wondering if we have such an unusual setup (a CoreOS guest under a Hyper-V host), such an unusual workload (Docker containers of Nginx, Gitlab, Redmine, MediaWiki, MariaDB) or a bad configuration. Any input / suggestion would be welcome.

The original error message (in the second instance) was:

Jun 05 02:00:50 localhost kernel: EXT4-fs error (device sda9): ext4_lookup:1595: inode #8347255: comm git: deleted inode referenced: 106338109
Jun 05 02:00:50 localhost kernel: Aborting journal on device sda9-8.
Jun 05 02:00:50 localhost kernel: EXT4-fs (sda9): Remounting filesystem read-only

At this point, an e2fsck run found lots of errors (didn't think to keep log) and placed about 357MB in lost+found for a 2TB partition with about 512GB data on it. The OS still bootes after this, so the lost parts seem to lie in user-data or docker containers.

Here are a few more details about the affected system:

$ uname -srm
Linux 4.19.123-coreos x86_64
$ sudo tune2fs -l /dev/sda9
tune2fs 1.45.5 (07-Jan-2020)
Filesystem volume name:   ROOT
Last mounted on:          /sysroot
Filesystem UUID:          04ab23af-a14f-48c8-af59-6ca97b3263bc
Filesystem magic number:  0xEF53
Filesystem revision #:    1 (dynamic)
Filesystem features:      has_journal ext_attr resize_inode dir_index filetype needs_recovery extent 64bit flex_bg inline_data 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:              533138816
Block count:              536263675
Reserved block count:     21455406
Free blocks:              391577109
Free inodes:              532851311
First block:              0
Block size:               4096
Fragment size:            4096
Group descriptor size:    64
Reserved GDT blocks:      15
Blocks per group:         32768
Fragments per group:      32768
Inodes per group:         32576
Inode blocks per group:   1018
Flex block group size:    16
Filesystem created:       Tue Sep 11 00:02:46 2018
Last mount time:          Fri Jun  5 15:40:01 2020
Last write time:          Fri Jun  5 15:40:01 2020
Mount count:              3
Maximum mount count:      -1
Last checked:             Fri Jun  5 08:14:10 2020
Check interval:           0 (<none>)
Lifetime writes:          79 GB
Reserved blocks uid:      0 (user root)
Reserved blocks gid:      0 (group root)
First inode:              11
Inode size:               128
Journal inode:            8
Default directory hash:   half_md4
Directory Hash Seed:      595db5c2-beda-4f32-836f-ee025416b0f1
Journal backup:           inode blocks

Update:

And a few more details about the host setup:

  • using Hyper-V Server 2016
  • the disk is based on a virtual disk file (as opposed to a physical disk)
  • the disk is setup to be dynamic (ie.e growing)
  • there are several snapshots/restore-points on the VM. I am not sure if this switches the disk image from dynamic to differencing(?)
filesystems hyper-v corruption ext4 coreos

1 Answers

  1. Best Answer

    What data orphaned inodes contains is a tricky enough problem. Why the storage system did such a thing is considerably more difficult.

    First, do incident response. Check if any of these workloads is having unplanned downtime. Evaluate your recovery options: any DR environment on separate storage, backups, other copies of the data.

    Consider making a backup of the VHD before changing anything. Allows undo of your actions, and perhaps you can let support examine the broken volume.

    Identify what data is affected.

    • Run file on those lost inodes to guess their format. Open and examine their contents.

    • Run integrity checks on the application data.

    Check everything in the storage and compute systems.

    • Storage array volume status: online, free capacity
    • Health of individual physical disks
    • Search guest logs for every message relating to EXT4
    • Run Windows Best Practices Analyzer. In the comments, we found a recommendation not to use VHD dynamic disks.

    There may not be an obvious cause. Even so, consider moving to a different system to rule out a hardware problem. If you have a DR system on different hardware, consider cutting over to that. Or try replacing smaller components, like disks in the array. Or migrate the VM to a different compute host.

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