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oceanBT
Asked: 2016-06-20 10:24:32 +0800 CST

How to find all volumes that btrfs df prints out?

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i don't understand where the second data "container" comes from:

ocean@nas:/mnt$ sudo btrfs filesystem df /
Data, RAID1: total=3.00GiB, used=1.70GiB
Data, single: total=1.00GiB, used=0.00B  <-- this one
System, RAID1: total=32.00MiB, used=16.00KiB
Metadata, RAID1: total=1.00GiB, used=73.86MiB
GlobalReserve, single: total=32.00MiB, used=0.00B

how can i find out where this comes from?

It suddenly appeared after balancing my drives:

  • new linux on btrfs filesystem, with two unbalanced hdds:

    ocean@nas:/mnt$ sudo btrfs filesystem df /
Data, single: total=2.01GiB, used=1.70GiB
System, DUP: total=8.00MiB, used=16.00KiB
Metadata, DUP: total=1.00GiB, used=72.38MiB
GlobalReserve, single: total=32.00MiB, used=0.00B

  • then i balanced the btrfs:

    ocean@nas:/mnt$ sudo btrfs balance start -dconvert=raid1 -mconvert=raid1 /
Done, had to relocate 5 out of 5 chunks

  • output after balacing: 

       ocean@nas:/mnt$ sudo btrfs filesystem show
   Label: 'hddArray1'  uuid: 925b7c82-f7da-4eda-89ce-990cc63f53ad
   Total devices 2 FS bytes used 1.77GiB
   devid    1 size 3.63TiB used 4.03GiB path /dev/sda3
   devid    2 size 3.64TiB used 5.03GiB path /dev/sdb

  • and (as above):

      ocean@nas:/mnt$ sudo btrfs filesystem df /
  Data, RAID1: total=3.00GiB, used=1.70GiB
  Data, single: total=1.00GiB, used=0.00B  <-- this one
  System, RAID1: total=32.00MiB, used=16.00KiB
  Metadata, RAID1: total=1.00GiB, used=73.86MiB
  GlobalReserve, single: total=32.00MiB, used=0.00B

  • and:

     ocean@nas:/mnt$ sudo btrfs device usage -g /
 /dev/sda3, ID: 1
   Device size:          3717.55GiB
   Data,RAID1:              3.00GiB
   Metadata,RAID1:          1.00GiB
   System,RAID1:            0.03GiB
   Unallocated:          3713.52GiB

 /dev/sdb, ID: 2
    Device size:          3726.02GiB
    Data,single:             1.00GiB
    Data,RAID1:              3.00GiB
    Metadata,RAID1:          1.00GiB
    System,RAID1:            0.03GiB
    Unallocated:          3720.99GiB

Thanks!

filesystem

1 Answers

  1. Best Answer

    You have different disk sizes. The difference is 1 GB.

    That is why there is 1GB "single" entry.

    The effect of this IMO will be that when the RAID is full, some data may be stored as "single".

    If you want to avoid this you can create a partition table on /dev/sdb and create there a partition exactly same size as /dev/sda3.

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