Re: [PATCH] btrfs-progs: add RAID5/6 support to btrfs fi us

[DanglingPointer <danglingpointerexception@gmail.com>]

Yes I do!

Please push/pressure to get this patch reviewed!

BR,
D.Pointer


On 26/3/20 7:12 am, Goffredo Baroncelli wrote:
> PING,
>
> does someone find interest on this kind of patch ?
>
> BR
> G.Baroncelli
>
> On 3/18/20 10:11 PM, Goffredo Baroncelli wrote:
>>
>> Hi all,
>>
>> this patch adds support for the raid5/6 profiles in the command
>> 'btrfs filesystem usage'.
>>
>> Until now the problem was that the value r_{data,metadata}_used is not
>> easy to get for a RAID5/6, because it depends by the number of disks.
>> And in a filesystem it is possible to have several raid5/6 chunks with a
>> different number of disks.
>>
>> In order to bypass this issue, I reworked the code to get rid of these
>> values where possible and to use the l_{data,metadata}_used ones.
>> Notably the biggest differences is in how the free space estimation
>> is computed. Before it was:
>>
>>     free_estimated = (r_data_chunks - r_data_used) / data_ratio;
>>
>> After it is:
>>
>>     free_estimated = l_data_chunks - l_data_used;
>>
>> which give the same results when there is no mixed raid level, but a
>> better result in the other case. I have to point out that before in the
>> code there was a comment that said the opposite.
>>
>> The other place where the r_{data,metadata}_used are use is for the
>> "Used:" field. For this case I estimated these values using the
>> following formula (only for raid5/6 profiles):
>>
>>     r_data_used += (double)r_data_chunks * l_data_used /
>>                                 l_data_chunks;
>>
>> Note that this is not fully accurate. Eg. suppose to have two raid5 
>> chunks,
>> the first one with 3 disks, the second one with 4 disks, and that each
>> chunk is 1GB.
>> r_data_chunks_r56, l_data_used_r56, l_data_chunks_r56 are completely 
>> defined,
>> but real r_data_used is completely different in these two cases:
>> - the first chunk is full and the second one id empty
>> - the first chunk is full empty and the second one is full
>> However now this error affect only the "Used:" field.
>>
>>
>> So now if you run btrfs fi us in a raid6 filesystem you get:
>>
>> $ sudo btrfs fi us /
>> Overall:
>>      Device size:          40.00GiB
>>      Device allocated:           8.28GiB
>>      Device unallocated:          31.72GiB
>>      Device missing:             0.00B
>>      Used:               5.00GiB
>>      Free (estimated):          17.36GiB    (min: 17.36GiB)
>>      Data ratio:                  2.00
>>      Metadata ratio:              0.00
>>      Global reserve:           3.25MiB    (used: 0.00B)
>>
>> Data,RAID6: Size:4.00GiB, Used:2.50GiB (62.53%)
>> [...]
>>
>> Instead before:
>>
>> $ sudo btrfs fi us /
>> WARNING: RAID56 detected, not implemented
>> WARNING: RAID56 detected, not implemented
>> WARNING: RAID56 detected, not implemented
>> Overall:
>>      Device size:          40.00GiB
>>      Device allocated:             0.00B
>>      Device unallocated:          40.00GiB
>>      Device missing:             0.00B
>>      Used:                 0.00B
>>      Free (estimated):             0.00B    (min: 8.00EiB)
>>      Data ratio:                  0.00
>>      Metadata ratio:              0.00
>>      Global reserve:           3.25MiB    (used: 0.00B)
>>
>> Data,RAID6: Size:4.00GiB, Used:2.50GiB (62.53%)
>> [...]
>>
>>
>> I want to point out that this patch should be compatible with my
>> previous patches set (the ones related to the new ioctl
>> BTRFS_IOC_GET_CHUNK_INFO). If both are merged we will have a 'btrfs 
>> fi us'
>> commands with full support a raid5/6 filesystem without needing root
>> capability.
>>
>> Comments are welcome.
>> BR
>> G.Baroncelli
>>
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