df shows wrong infos on btrfs raid (5gb and 3gb hdd)

[Bernd Kohler <kohler@umic.rwth-aachen.de>]

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Hi,

this is not really a bug in btrfs but to spread the info I will just
drop this short message:

My System (VirtualBox VM, 3 virtual HDDs with 10G, 5G and 3G) is today
installed Ubuntu 12.04 LTS 64bit with Kernel 3.2.0-26 generic, a
/dev/sda hdd containing /boot with ext4 and / with btrfs.

After installation update/upgrade process I created a new partition on
/dev/sdb and /dev/sdbc with max available size - 5G for sdb1 and 3G for
sdc1.

Now I made my RAID:
mkfs.btrfs -L MYRAID -d raid1 -m raid1 /dev/sdb1 /sdc1

and made this RAID available to the filesystem
mount /dev/sdc1 /mnt

The infos, given by "btrfs fi show  /dev/sdb1" and "btrfs fi df /mnt"
are ok, but df is "lieing":

Filesystem Size Used Avail Use% Mounted on
/dev/sdc1  8.0G 5.2G 56k   100% /mnt

Don't get confused about used space, tried to write a 4G file on this
RAID, which ended with "write error: no space left on device" - as expected

FYI

best

Bernd Kohler

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UMIC - RWTH Aachen
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