Share size misrepresented for Samba

Bugs
1

Hi,

i just created a 3 drive RAID5 array from 3TB drives. Thus it is ~8.1TiB of total disk space, from which i have ~5.4TB usable.

This is represented mostly correctly on web interface:
Shares: 5.49 TB Capacity
Pools: 5.46TB Capacity + 2.64TB Raid overhead
Disks: 8.12TB

All fine so far. Unfortunately when i mount the share under a letter in Windows 10, it shows that the share has a size 8.18TB.

Or is it down to the fact that the command line tools are misrepresenting these numbers as well, and Samba just reports the size reported by the OS ?
[root@nas ~]# df -h
Filesystem Size Used Avail Use% Mounted on
…
/dev/sda 8.2T 50G 8.2T 1% /mnt2/MediaPool
/dev/sda 8.2T 50G 8.2T 1% /mnt2/Media

[root@nas ~]# btrfs fi usage /mnt2/Media
WARNING: RAID56 detected, not implemented
WARNING: RAID56 detected, not implemented
WARNING: RAID56 detected, not implemented
Overall:
Device size: 8.19TiB
Device allocated: 0.00B
Device unallocated: 8.19TiB
Device missing: 0.00B
Used: 0.00B
Free (estimated): 0.00B (min: 8.00EiB)
Data ratio: 0.00
Metadata ratio: 0.00
Global reserve: 16.00MiB (used: 0.00B)

Thanks

Edit: On other side the disk use increases by the parity data too, so while it is a bit weird that it represents 8.1TB instead of 5.4TB, at same time percentually it is showing the correct disk use. Incorrect in absolute numbers (GB), correct in relative numbers (%).

2

I’m willing to bet it is because the CLI tools for RAID56 do not work properly yet. They don’t yet report free space on 5/6 arrary’s. Notice how it says that the free space is 0?

3

Yes, it is because of what BTRFS reports (incorrectly) to the actual system.

For example right now it says :
/dev/sda 8.2T 1.4T 6.2T 19% /mnt2/MediaPool

That is 1.4TiB used from 8.2TiB, but only 6.2TiB is available, because of the parity drive using up the remaining 600GB, just as the btrfs fi usage says futher down :
Data,RAID5: Size:1.37TiB, Used:1.36TiB
/dev/sda 701.00GiB
/dev/sdb 701.00GiB
/dev/sdc 701.00GiB

Well, let’s hope btrfs devs will fix this sometime in future :). Parity space should lower both total and available disk space in what is reported to the OS.

4

Yep one of the problems left with the RAID 5/6 implements in BTRFS. It has been hashed out pretty well over here If you would like to take a look.