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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