Re: CRC mismatch

[Chris Murphy <lists@colorremedies.com>]

On Tue, Oct 16, 2018 at 9:42 AM, Austin S. Hemmelgarn
<ahferroin7@gmail.com> wrote:
> On 2018-10-16 11:30, Anton Shepelev wrote:
>>
>> Hello, all
>>
>> What may be the reason of a CRC mismatch on a BTRFS file in
>> a virutal machine:
>>
>>     csum failed ino 175524 off 1876295680 csum 451760558
>>     expected csum 1446289185
>>
>> Shall I seek the culprit in the host machine on in the guest
>> one?  Supposing the host machine healty, what operations on
>> the gueest might have caused a CRC mismatch?
>>
> Possible causes include:
>
> * On the guest side:
>   - Unclean shutdown of the guest system (not likely even if this did
> happen).
>   - A kernel bug on in the guest.
>   - Something directly modifying the block device (also not very likely).
>
> * On the host side:
>   - Unclean shutdown of the host system without properly flushing data from
> the guest.  Not likely unless you're using an actively unsafe caching mode
> for the guest's storage back-end.
>   - At-rest data corruption in the storage back-end.
>   - A bug in the host-side storage stack.
>   - A transient error in the host-side storage stack.
>   - A bug in the hypervisor.
>   - Something directly modifying the back-end storage.
>
> Of these, the statistically most likely location for the issue is probably
> the storage stack on the host.

Is there still that O_DIRECT related "bug" (or more of a limitation)
if the guest is using cache=none on the block device?

Anton what virtual machine tech are you using? qemu/kvm managed with
virt-manager? The configuration affects host behavior; but the
negative effect manifests inside the guest as corruption. If I
remember correctly.

-- 
Chris Murphy