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

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

[Bernd Kohler]

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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

-- 
UMIC - RWTH Aachen
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Re: df shows wrong infos on btrfs raid (5gb and 3gb hdd)

[Martin Steigerwald]

Am Mittwoch, 4. Juli 2012 schrieb Bernd Kohler:
> Hi,

Hi Bernd,

> 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
[…]
> 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

First read and understand:

https://btrfs.wiki.kernel.org/index.php/FAQ#Help.21_Btrfs_claims_I.27m_out_of_space.2C_but_it_looks_like_I_should_have_lots_left.21

Then re-examine your situation.

If you still think BTRFS is lying or have a good suggestion on how to 
change the current situation, post it here.

Thanks,
-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7

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

[Martin Steigerwald]

Am Mittwoch, 4. Juli 2012 schrieb Bernd Kohler:
> 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

+ post outputs of btrfs fi sh and btrfs fi df

Only with these in mind it is possible to say anything about the df 
output.

-- 
Martin 'Helios' Steigerwald - http://www.Lichtvoll.de
GPG: 03B0 0D6C 0040 0710 4AFA  B82F 991B EAAC A599 84C7