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

[Anand Jain <anand.jain@oracle.com>]

On 09/20/2015 08:31 AM, Qu Wenruo wrote:
>
>
> 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,

  in this case the read chunk would anyway fail, right ?
  and that will lead to mount fail.

Thanks, Anand

> 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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