BTRFS 3-disk RAID1 only having partial capacity

[Gasur]

I am unable to get the full capacity of BTRFS 3-disk RAID1, which in my case (3x400GB) should yield 600GB of available space according to https://carfax.org.uk/btrfs-usage/.

 

Oddly enough, the attached screenshot shows the array size as 600GB as it should, however, the used space does not correlate with the "progress bar" and the free space only states 400GB, as if one of the disks were not in use.

 

I looked at df which showed the same:

 

Filesystem			Size	Used	Avail	Use%	Mounted on
/dev/mapper/sdd1  	559G  	1.2G  	374G   	1% 		/mnt/cache

I also confirmed that it is in fact RAID1 for data and metadata:

Quote

Data, RAID1: total=25.00GiB, used=24.88GiB
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=1.00GiB, used=28.91MiB
GlobalReserve, single: total=23.72MiB, used=0.00B

In case it was purely a visual bug, I attempted to write data to the array, however it used up disk space and did not show the true available disk space.

 

Edited May 11, 2021 by Gasur

[JorgeB]

1 hour ago, Gasur said:

am unable to get the full capacity of BTRFS 3-disk RAID1

It's a known btrfs bug with an odd number of devices in raid1, but just the reported free space is wrong, you can still use the full capacity, and free space will be less wrong as the pool gets filled.