Re: [PATCH 2/2] btrfs: Remove unneeded missing device number check

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

在 2015年09月18日 14:45, Anand Jain 写道:
>
> Hi Qu,
>
>   Thanks for the comments on patch [1].
>
>> For example, if one use single metadata for 2 disks,
>  > and each disk has one metadata chunk on it.
>
>   how that can be achieved ?
By this, I mean, the metadata profile is SINGLE,
and there is 2 metadata chunks.

One on disk1 and one on disk2.

As btrfs chunk allocate will always use device by avaiable space order,
it should be quite easy to archieve that situation.

In that case, any missing device will be a disaster, and it's better not 
to allow RW mount.

Thanks,
Qu
>
>> One device got missing later.
>
>   it would surely depend on which one of the device ? (initial only
> devid 1 mountable, with other missing)
>
>
> Thanks, Anand
>
>> Then your patch will allow the fs to be mounted as rw, even some tree
>> block can be in the missing device.
>> For RO case, it won't be too dangerous, but if we mounted it as RW, who
>> knows what will happen.
>> (Normal tree COW thing should fail before real write, but I'm not sure
>> about other RW operation like scrub/replace/balance and others)
>>
>> And I think that's the original design concept behind the old missing
>> device number check, and it's not a bad idea to follow it anyway.
>>
>> For the patch size, I find a good idea to handle it, and should make the
>> patch(set) size below 200 lines.
>>
>> Further more, it's even possible to make btrfs change mount option to
>> degraded for runtime device missing.
>>
>> Thanks,
>> Qu
>>>
>>>   I tried to break both the approaches (this patch set and [1]) but I
>>> wasn't successful. sorry if I am missing something.
>>>
>>> Thanks, Anand
>>>
>>> [1] [PATCH 23/23] Btrfs: allow -o rw,degraded for single group profile
>
>
>
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