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ua4000

Member

Registered: 2015-10-14

Posts: 566

BTRFS nursing - balance

usage: btrfs balance start [options] <path>

balance wants a btrfs mountpoint, not a device.

But the wiki states: "A balance passes all data in the filesystem through the allocator again."
This sounds like the whole btrfs volume is meant?

So the question rises (on a btrfs volume with multiple subvolumes): does balance work only on the mountpoint and below, or on the whole btrfs volume?

thanks very much

Last edited by ua4000 (2016-11-05 10:59:26)

ua4000

Member

Registered: 2015-10-14

Posts: 566

Re: BTRFS nursing - balance

I have thought about it and did a testcase:

/ and /home and /data are subvolumes on one partition:

sudo btrfs balance start -v --full-balance /

sudo btrfs balance status /home
Balance on '/home' is running
0 out of about 97 chunks balanced (1 considered), 100% left

sudo btrfs balance status /
Balance on '/' is running
1 out of about 97 chunks balanced (2 considered),  99% left

sudo btrfs balance status /data
Balance on '/data' is running
1 out of about 97 chunks balanced (2 considered),  99% left

As you can see, quering the balance status gives exact 97 chunks for all subvolume, you can query /home while / was started. And: balance cancel works on /home even if it was started with /.

So I think the answer is: balance is doing the whole volume including all subvolumes.

Is my conclusion correct?