Re: btrfs ontop of LVM ontop of MD RAID1 supported?

[Nigel Kukard <nkukard@LBSD.net>]

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Hi there Roman,

On 3/2/24 15:47, Roman Mamedov wrote:
> On Sat, 2 Mar 2024 15:01:43 +0000
> Nigel Kukard <nkukard@LBSD.net> wrote:
>
>> I'm wondering if btrfs ontop of LVM ontop of MD RAID1 is supported?
> Should be absolutely supported.
>
>> I've managed to reproduce with 100% accuracy severe data corruption
>> using this configuration on 6.6.19.
>>
>> 2 x 1.92T NVMe's in MD RAID1 configuration
>> LVM volume created ontop of the MD RAID1
>> btrfs filesystem on the LV
>>
>> I then write about 100-200G of data. Create a snapshot. Read/write the
>> file and get these messages...
> Has the MD RAID1 finished its initial sync after creation?
>
> Have you tried waiting until it finishes and only then do thewrites to see if
> the corruption is still observed (of course that's in no way a "workaround",
> just to see what might cause the bug).

Sync completed on all 4 systems I tested on before creating the LVM 
volume and filesystem.


>
> Do you know any kernel versions or series where this corruption did not happen?
>
> I assume you're not saying it appeared in 6.6.19 compared to 6.6.18.

Sadly, this is the first time I'm testing this specific setup. These are 
production systems, so changing kernel version is a bit tricky.

Let me try reproduce it on another bit of hardware, I'll revert back.


>
> Can you try the 6.1 series? Or maybe also 6.8?

Sure, let me see if I can set something up and reproduce it, then we can 
test different kernel versions and start bisecting.


> I made a Btrfs on top of LVM on top of RAID1 myself now, but on consumer SSDs.
> Copying some files to it now, to check. Would be also helpful if you can find
> a precise sequence of commands which can trigger the bug, less vague than
> copy some files to it and see.

Sure thing. Let me see if I can trim things down and get a simple 
sequence of commands to make things easier.

-N


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