Re: Filesystem Went Read Only During Raid-10 to Raid-6 Data Conversion

[Steven Davies <btrfs-list@steev.me.uk>]

On 2020-07-21 21:48, Goffredo Baroncelli wrote:
> On 7/21/20 12:15 PM, Steven Davies wrote:
>> On 2020-07-20 18:57, Goffredo Baroncelli wrote:
>>> On 7/18/20 12:36 PM, Steven Davies wrote:

>>>>>> /dev/sdf, ID: 12
>>>>>>     Device size:             9.10TiB
>>>>>>     Device slack:              0.00B
>>>>>>     Data,RAID10:           784.31GiB
>>>>>>     Data,RAID10:             4.01TiB
>>>>>>     Data,RAID10:             3.34TiB
>>>>>>     Data,RAID6:            458.56GiB
>>>>>>     Data,RAID6:            144.07GiB
>>>>>>     Data,RAID6:            293.03GiB
>>>>>>     Metadata,RAID10:         4.47GiB
>>>>>>     Metadata,RAID10:       352.00MiB
>>>>>>     Metadata,RAID10:         6.00GiB
>>>>>>     Metadata,RAID1C3:        5.00GiB
>>>>>>     System,RAID1C3:         32.00MiB
>>>>>>     Unallocated:            85.79GiB
>>>>> 
>>> [...]
>>>> 
>>>> RFE: improve 'dev usage' to show these details.
>>>> 
>>>> As a user I'd look at this output and assume a bug in btrfs-tools 
>>>> because of the repeated conflicting information.
>>> 
>>> What would be the expected output ?
>>> What about the example below ?
>>> 
>>>  /dev/sdf, ID: 12
>>>      Device size:             9.10TiB
>>>      Device slack:              0.00B
>>>      Data,RAID10:           784.31GiB
>>>      Data,RAID10:             4.01TiB
>>>      Data,RAID10:             3.34TiB
>>>      Data,RAID6[3]:         458.56GiB
>>>      Data,RAID6[5]:         144.07GiB
>>>      Data,RAID6[7]:         293.03GiB
>>>      Metadata,RAID10:         4.47GiB
>>>      Metadata,RAID10:       352.00MiB
>>>      Metadata,RAID10:         6.00GiB
>>>      Metadata,RAID1C3:        5.00GiB
>>>      System,RAID1C3:         32.00MiB
>>>      Unallocated:            85.79GiB
>> 
>> That works for me for RAID6. There are three lines for RAID10 too - 
>> what's the difference between these?
> 
> The differences is the number of the disks involved. In raid10, the
> first 64K are on the first disk, the 2nd 64K are in the 2nd disk and
> so until the last disk. Then the n+1 th 64K are again in the first
> disk... and so on.. (ok I missed the RAID1 part, but I think the have
> giving the idea )
> 
> So the chunk layout depends by the involved number of disk, even if
> the differences is not so dramatic.

Is this information that the user/sysadmin needs to be aware of in a 
similar manner to the original problem that started this thread? If not 
I'd be tempted to sum all the RAID10 chunks into one line (each for data 
and metadata).

>>>     Data,RAID6:        123.45GiB
>>>         /dev/sda     12.34GiB
>>>         /dev/sdb     12.34GiB
>>>         /dev/sdc     12.34GiB
>>>     Data,RAID6:        123.45GiB
>>>         /dev/sdb     12.34GiB
>>>         /dev/sdc     12.34GiB
>>>         /dev/sdd     12.34GiB
>>>         /dev/sde     12.34GiB
>>>         /dev/sdf     12.34GiB
>> 
>> Here there would need to be something which shows what the difference 
>> in the RAID6 blocks is - if it's the chunk size then I'd do the same 
>> as the above example with e.g. Data,RAID6[3].
> 
> We could add a '[n]' for the profile where it matters, e.g. raid0,
> raid10, raid5, raid6.
> What do you think ?

So like this? That would make sense to me, as long as the meaning of [n] 
is explained in --help or the manpage.
      Data,RAID6[3]:     123.45GiB
          /dev/sda     12.34GiB
          /dev/sdb     12.34GiB
          /dev/sdc     12.34GiB
      Data,RAID6[5]:     123.45GiB
          /dev/sdb     12.34GiB
          /dev/sdc     12.34GiB
          /dev/sdd     12.34GiB
          /dev/sde     12.34GiB
          /dev/sdf     12.34GiB

-- 
Steven Davies