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adamc83

Member

Registered: 2008-06-01

Posts: 41

btrfs disk usage questions

I have my root partition in btrfs (yes, I know its in heavy development), and I have a few questions on disk usage...

I have a ~30GB device:

#btrfs-show
Total devices 1 FS bytes used 13.28GB
devid    1 size 29.77GB used 29.77GB path /dev/sdc2

with somehow under 19GB of usuable space:

$btrfs filesystem df /
Data: total=18.74GB, used=12.96GB
Metadata: total=5.51GB, used=328.75MB
System: total=12.00MB, used=4.00KB

Two questions:
1) 18.74 + 5.51 = 24.25, not 29.77. I dont have any snapshots or subvolumes. Where's my missing ~5.5GB? This is curiously almost the exact size of the metadata area, are there two copies?

2) The metadata area is seemingly never more than 10% full, leading to a waste of space IMO. Is there a way to reduce its size? There are apparently (meta)data profiles that can be used during formatting, though I cant find what they do.

If I can fix any of these issues without reformatting that would be great. I'd rather not have to reformat if I can avoid it, though its not a huge deal.

karol

Archivist

Registered: 2009-05-06

Posts: 25,440

Re: btrfs disk usage questions

Is df showing correct numbers for btrfs? I know it had some issues, I don't know if they're fixed now.

Edit: Their wiki seems down arm, but you can try 'btrfs-show' and see how much is it reporting.

Last edited by karol (2010-08-22 19:35:04)

Spacenick

Member

From: Germany

Registered: 2010-04-02

Posts: 168

Re: btrfs disk usage questions

When btrfs is in mirror mode df will double all byte counts thus making the percentage correct but it lists twice the capacity