On Sun, Aug 19, 2012 at 02:08:17PM +0000, Daniel Pocock wrote: > > > I created a 1TB RAID1. So far it is just for testing, no important data > on there. > > > After a reboot, I tried to mount it again > > # mount /dev/mapper/vg00-btrfsvol0_0 /mnt/btrfs0 > mount: wrong fs type, bad option, bad superblock on > /dev/mapper/vg00-btrfsvol0_0, > missing codepage or helper program, or other error > In some cases useful info is found in syslog - try > dmesg | tail or so
With multi-volume btrfs filesystems, you have to run "btrfs dev
scan" before trying to mount it. Usually, the distribution will do
this in the initrd (if you've installed its btrfs-progs package).
> Then I did btrfsck - it reported no errors, but mounted OK:
>
> # btrfsck /dev/mapper/vg00-btrfsvol0_0
[...]
The first thing that btrfsck does is to do a device scan.
[...]
> Can anyone comment on this?
See above.
> Also, df is reporting double the actual RAID1 volume size, and double
> the amount of data stored in this filesystem:
>
> # df -lh .
> Filesystem Size Used Avail Use% Mounted on
> /dev/mapper/vg00-btrfsvol0_0 1.9T 51G 1.8T 3% /mnt/btrfs0
>
> I would expect to see Size=1T, Used=25G
>
> # strace -v -e trace=statfs df -lh /mnt/btrfs0
> statfs("/mnt/btrfs0", {f_type=0x9123683e, f_bsize=4096,
> f_blocks=488374272, f_bfree=475264720, f_bavail=474749786, f_files=0,
> f_ffree=0, f_fsid={2083217090, -1714407264}, f_namelen=255,
> f_frsize=4096}) = 0
> Filesystem Size Used Avail Use% Mounted on
> /dev/mapper/vg00-btrfsvol0_0 1.9T 51G 1.8T 3% /mnt/btrfs0
This is an FAQ:
https://btrfs.wiki.kernel.org/index.php/FAQ#Why_is_free_space_so_complicated.3F
tl;dr: It's reporting the total number of raw storage bytes,
because it's impossible to compute actual usable space in the general
case.
Hugo.
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