Re: CRC mismatch

["Austin S. Hemmelgarn" <ahferroin7@gmail.com>]

On 2018-10-16 16:27, Chris Murphy wrote:
> 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?
I had actually forgotten about this, and I'm not quite sure if it's 
fixed or not.
> 
> 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.
>