Re: Two partitionless BTRFS drives no longer seen as containing BTRFS filesystem

[Qu Wenruo <quwenruo.btrfs@gmx.com>]

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On 2018/10/7 下午2:47, evan d wrote:
>> None of your super blocks has correct magic.
> 
> 
> I take it this applies to both drives?

Yes, both drivers have something wrong.

> 
> 
> 
>> This means either your whole disk get corrupted, or something introduced
>> some offset.
>>
>> Please try the following commands to dump more data around super blocks,
>> so we could be able to find the possible offset:
>>
>> # dd if=/dev/sdb of=possible_sb_range.raw bs=1M count=128
>> # grep -obUaP "\x5F\x42\x48\x52\x66\x53\x5F\x4D" possible_sb_range.
>>
>> For a valid btrfs without any offset, the result should look like:
>> 65600:_BHRfS_M
>> 67108928:_BHRfS_M
> 
> # dd if=/dev/sdc of=possible_sb_range.sdc.raw bs=1M count=128
> 128+0 records in
> 128+0 records out
> 134217728 bytes (134 MB, 128 MiB) copied, 0.737479 s, 182 MB/s
> 
> # dd if=/dev/sdb of=possible_sb_range.sdb.raw bs=1M count=128
> 128+0 records in
> 128+0 records out
> 134217728 bytes (134 MB, 128 MiB) copied, 0.726327 s, 185 MB/s
> 
> # grep -obUaP "\x5F\x42\x48\x52\x66\x53\x5F\x4D" possible_sb_range.sdb.raw
> # grep -obUaP "\x5F\x42\x48\x52\x66\x53\x5F\x4D" possible_sb_range.sdc.raw
> 
> Both return nothing.

Then this is not good at all.

The super blocks should be at 64K and 64M.
If first 128M doesn't hit, I highly doubt something more strange happened.

> 
> Both drives pass S.M.A.R.T. testing so I'd have to think the
> corruption stems from some kind of offset rather than random
> corruption.

Corruption shouldn't happen like this.

And offset shouldn't be so large to offset the whole 128M range.

I'm considering something like encryption.
Maybe the disk is already encrypted by hardware?

>  They may have accidentally been inserted into a Windows
> machine (but not partitioned or formatted).  Could this be a likely
> cause?

Windows is just a black box, I have no idea what a Windows could do to a
disk.

But it doesn't explain why the 2nd super block can't be located, unless
Windows is wipe more data than the first 128M.

If the disk is larger than 256G, would you please try to locate the last
possible super at 256G?

# dd if=/dev/sdb bs=1M of=last_chance.raw count=128 skip=256M
# grep -obUaP "\x5F\x42\x48\x52\x66\x53\x5F\x4D" last_chance.raw

If still no hit, you could try just run the grep command on the disk.
It would take a long long time reading all data from the disk.

If still no hit, it means definitely not some easy offset.

Thanks,
Qu
> 


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