Weird free space issues...

[joe_schmo]

So my /data partition shows:

Filesystem     Size     Used    Avail   Use%    Mounted on
/dev/md127    37T      32T     4.9T    87%      /data

In the UI, on the Volume page it shows:

data 31.4TB

Free: 4.83 TB

If I hover over the pie chart it says:

Data 31.22/35.40 TB

Metadata 38.93/105.54 GB

Free 476 GB

Why is the pie chart hover showing only 476GB free?

[joe_schmo]

[joe_schmo]

I added a screenshot of what I am seeing... anyone have any ideas?

[joe_schmo]

root@NAS:~# btrfs fi show /data
Label: '7c6e0558:data'  uuid: c87b4989-dcf4-46e2-9029-43c618569319
        Total devices 4 FS bytes used 32.11TiB
        devid    1 size 13.62TiB used 13.62TiB path /dev/md127
        devid    2 size 4.55TiB used 4.55TiB path /dev/md126
        devid    3 size 9.10TiB used 9.09TiB path /dev/md125
        devid    4 size 9.10TiB used 9.09TiB path /dev/md124

root@NAS:~# btrfs fi df /data
Data, single: total=36.14TiB, used=32.07TiB
System, RAID1: total=32.00MiB, used=304.00KiB
System, DUP: total=8.00MiB, used=4.40MiB
Metadata, RAID1: total=29.00GiB, used=28.60GiB
Metadata, DUP: total=76.50GiB, used=11.12GiB
GlobalReserve, single: total=512.00MiB, used=0.00B

[joe_schmo]

anyone?

[mdgm-ntgr]

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The free in the latter case is referring to unallocated space, which is quite a different thing.

If you sum up the unused allocation with the unallocated space you'll get a figure a lot closer to the space free on your volume: 35.40TB - 31.22 TB + 105.54 - 38.93GB + 476GB

Space is allocated to data and metadata as needed. If a chunk is emptied that space is returned to unallocated space.

Your data volume is getting quite full btw. You may wish to consider removing some files or expanding your data volume.

[joe_schmo]

Right, OK... but in that screen shot , the left side, data, shows only GBs free, not TB.

Why?

[joe_schmo]

I mean, hovering over it shows 13GB free but the graph shows 4TB free.  

[StephenB]

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@joe_schmo wrote:

I mean, hovering over it shows 13GB free but the graph shows 4TB free.  

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"free" is a confusing concept with BTRFS.

There is 

• allocated and used space
• allocated but unused space
• unallocated and unused space.

You have ~13 GB of unallocated and unused space, and about ~4TB of allocated but unused space.

You can start running into trouble when you exceed about 85% allocated+used space, and you are running around 88% full.  So you might want to free up some space (perhaps delete some snapshots if you use them).

You also should run a balance from the volume settings wheel.