[linux-lvm] Thin provisioned pool errors

[Timur Alperovich]

Hi all,

We are using LVM thin in EC2 and recently bumped into an error that seems
to indicate metadata corruption. I was hoping someone on the list could
clarify what likely happened and point to what we could do to avoid this in
the future (any recent patches or other work).

The error is the following:
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947135]
device-mapper: thin: dm_thin_insert_block() failed
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947153] Buffer
I/O error on device dm-315, logical block 2430188
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947164] Buffer
I/O error on device dm-315, logical block 2430189
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947169] Buffer
I/O error on device dm-315, logical block 2430190
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947174] Buffer
I/O error on device dm-315, logical block 2430191
Sep 27 20:09:37 magtest-ferenc-307-820-3 kernel: [2076275.947182] EXT4-fs
warning (device dm-315): ext4_end_bio:317: I/O error writing to inode
1305621 (offset 2429468672 size 16384 starting block 2430188)

The failure in dm_thin_insert_block() repeats 10 times and is followed by
the following message:
Sep 27 20:09:41 magtest-ferenc-307-820-3 kernel: [2076279.600905]
device-mapper: thin: dm_thin_get_highest_mapped_block returned -61

The device mapper error is repeated until the VM was taken offline and the
EBS volumes snapshotted. At this point, running thin_check, produces the
following:
examining superblock
examining devices tree
  missing devices: [159, 277]
    bad checksum in btree node
examining mapping tree
  missing all mappings for devices: [229, 229]
    bad checksum in btree nodeunknown node typeunknown node typeunknown
node typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node typeunknown node
typeunknown node typeunknown node typeunknown node type
  thin device 230 is missing mappings [57251, -]
    invalid key

The missing mappings error is repeated for many devices.

At this point, would going through the steps of thin_dump/thin_repair
remedy this?

Is there any additional information I can get from the system to understand
what happened? I wonder if there was an issue with the underlying EBS
storage, but have no way of confirming that at the moment.

Lastly, this is Ubuntu 12.04 LTS. I did pull in the thin provisioning tools
version 0.3.1, but the kernel is 3.8.0 (3.8.0-32-generic) and LVM2 package
is:
  LVM version:     2.02.98(2) (2012-10-15)
  Library version: 1.02.77 (2012-10-15)

Are there known patches that we may be missing that would remedy some of
these issues?

Thank you,
Timur
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