On Monday, 13 April 2020 10:08:50 UTC Joshua Houghton wrote:
> On Wednesday, 18 March 2020 21:11:56 UTC 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
>
> Hi Goffredo
>
> Thanks you for this. It's something I've been wanting for a while. Do
> you know why I get significantly different results in the overall summary
> when I do not run it as root. I'm not sure if this is a bug or a
> limitation.
>
> When I run it as root it looks to be showing the correct values.
>
> joshua@r2400g:~/development/btrfs-progs$ colordiff -u <(./btrfs fi us
> /mnt/raid/) <(sudo ./btrfs fi us /mnt/raid/) WARNING: cannot read detailed
> chunk info, per-device usage will not be shown, run as root --- /dev/fd/63
> 2020-04-13 10:54:26.833747190 +0100
> +++ /dev/fd/62 2020-04-13 10:54:26.843746984 +0100
> @@ -1,17 +1,32 @@
> Overall:
> Device size: 29.11TiB
> - Device allocated: 284.06GiB
> - Device unallocated: 28.83TiB
> - Device missing: 29.11TiB
> - Used: 280.99GiB
> - Free (estimated): 0.00B (min: 14.95TiB)
> - Data ratio: 0.00
> + Device allocated: 19.39TiB
> + Device unallocated: 9.72TiB
> + Device missing: 0.00B
> + Used: 18.67TiB
> + Free (estimated): 7.82TiB (min: 5.39TiB)
> + Data ratio: 1.33
> Metadata ratio: 2.00
> Global reserve: 512.00MiB (used: 0.00B)
>
> Data,RAID5: Size:14.33TiB, Used:13.80TiB (96.27%)
> + /dev/mapper/traid3 4.78TiB
> + /dev/mapper/traid1 4.78TiB
> + /dev/mapper/traid2 4.78TiB
> + /dev/mapper/traid4 4.78TiB
>
> Metadata,RAID1: Size:142.00GiB, Used:140.49GiB (98.94%)
> + /dev/mapper/traid3 63.00GiB
> + /dev/mapper/traid1 64.00GiB
> + /dev/mapper/traid2 63.00GiB
> + /dev/mapper/traid4 94.00GiB
>
> System,RAID1: Size:32.00MiB, Used:1.00MiB (3.12%)
> + /dev/mapper/traid1 32.00MiB
> + /dev/mapper/traid4 32.00MiB
>
> +Unallocated:
> + /dev/mapper/traid3 2.44TiB
> + /dev/mapper/traid1 2.44TiB
> + /dev/mapper/traid2 2.44TiB
> + /dev/mapper/traid4 2.41TiB
>
>
> This is in contrast to raid1 which seems to be mostly correct, irrespective
> of what user I run as.
>
>
> joshua@arch:/var/joshua$ colordiff -u <(btrfs fi us raid/) <(sudo btrfs fi
> us raid/) WARNING: cannot read detailed chunk info, per-device usage will
> not be shown, run as root --- /dev/fd/63 2020-04-13 09:52:54.630750079
> +0000
> +++ /dev/fd/62 2020-04-13 09:52:54.637416835 +0000
> @@ -2,7 +2,7 @@
> Device size: 8.00GiB
> Device allocated: 1.32GiB
> Device unallocated: 6.68GiB
> - Device missing: 8.00GiB
> + Device missing: 0.00B
> Used: 383.40MiB
> Free (estimated): 3.55GiB (min: 3.55GiB)
> Data ratio: 2.00
> @@ -10,8 +10,17 @@
> Global reserve: 3.25MiB (used: 0.00B)
>
> Data,RAID1: Size:409.56MiB, Used:191.28MiB (46.70%)
> + /dev/loop0 409.56MiB
> + /dev/loop1 409.56MiB
>
> Metadata,RAID1: Size:256.00MiB, Used:416.00KiB (0.16%)
> + /dev/loop0 256.00MiB
> + /dev/loop1 256.00MiB
>
> System,RAID1: Size:8.00MiB, Used:16.00KiB (0.20%)
> + /dev/loop0 8.00MiB
> + /dev/loop1 8.00MiB
>
> +Unallocated:
> + /dev/loop0 3.34GiB
> + /dev/loop1 3.34GiB
>
> Does anyone know if this is something we can fix? I'm happy to take a look.
>
> Joshua Houghton
Sorry missed this last bit never mind
> If both are merged we will have a 'btrfs fi us'
> commands with full support a raid5/6 filesystem without needing root
> capability.
