kernel .32, btrfs-vol -b, why is metadata=data

kernel .32, btrfs-vol -b, why is metadata=data

[Ahmed Kamal]

Hi everyone,

I'm running kernel 2.6.32-0.65.rc8.git5.fc13.x86_64. And I ran
"btrfs-vol -b", however for 10G of data I still have 9G of metadata!
How do I fix this ?

[root@matrix ~]# btrfs-vol -b /
ioctl returns 0
You have mail in /var/spool/mail/root
[root@matrix ~]# btrfs-show
failed to read /dev/sr0
Label: none  uuid: 06b0d069-b1cb-48c4-b26f-c5088a2360d2
        Total devices 1 FS bytes used 10.43GB
        devid    1 size 25.72GB used 19.02GB path /dev/dm-1

Btrfs Btrfs v0.19

Re: kernel .32, btrfs-vol -b, why is metadata=data

[Chris Mason]

On Sun, Dec 06, 2009 at 10:50:45AM +0200, Ahmed Kamal wrote:
> Hi everyone,
> 
> I'm running kernel 2.6.32-0.65.rc8.git5.fc13.x86_64. And I ran
> "btrfs-vol -b", however for 10G of data I still have 9G of metadata!
> How do I fix this ?
> 
> [root@matrix ~]# btrfs-vol -b /
> ioctl returns 0
> You have mail in /var/spool/mail/root
> [root@matrix ~]# btrfs-show
> failed to read /dev/sr0
> Label: none  uuid: 06b0d069-b1cb-48c4-b26f-c5088a2360d2
>         Total devices 1 FS bytes used 10.43GB
>         devid    1 size 25.72GB used 19.02GB path /dev/dm-1

Used means something different here than it does to df.  It just means
that we've preallocated 19GB of space on the drive as either data or
metadata, but it doesn't say if that space is actively used by the FS
yet or not.

In other words, btrfs-show could tell you that 19GB has been used, but
df could say that 0 bytes are in use in the FS.  This is because btrfs
allocates from devices to create chunks at a specific raid level and
then does suballocations inside those chunks.

-chris

Re: kernel .32, btrfs-vol -b, why is metadata=data

[Ahmed Kamal]

> In other words, btrfs-show could tell you that 19GB has been used, but
> df could say that 0 bytes are in use in the FS.

Thanks Chris for the clarification. So despite saying 19G are used, I
shouldn't be worried about running out of disk space, since these are
just pre-allocated areas. Perhaps btrfs-show should show how much
areas are really used, besides how much are just pre-allocated. The
thing is, I keep monitoring that number to avoid ENOSPC and now I know
that number is not accurate.

Thanks for the stellar work
Regards