Tag - file system - Ludo's notes

Why does btrfs show up twice the capacity available?

By Ludovic Francois on Thursday, December 15 2011, 20:52

If you decide to use the btrfs data (or/and metadata) replication, you will see the df command reports you your storage get used twice as fast as you expect. Btrfs doesn't act as for example mdadm. Each file will get striped at the block level across all devices available depending on the replication policy selected.

Create a new test file system

root@blackbox:~# mkfs.btrfs -m raid1 -d raid1 -L btrfs01 /dev/sdb /dev/sdc

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

adding device /dev/sdc id 2
fs created label btrfs01 on /dev/sdb
     nodesize 4096 leafsize 4096 sectorsize 4096 size 298.02GB
Btrfs Btrfs v0.19
root@blackbox:~#

Mount it

root@blackbox:~# mkdir /mnt/btrfs01

root@blackbox:~# mkdir /mnt/btrfs01
root@blackbox:~# mount /dev/sdb /mnt/btrfs01/

Check the capacity available

root@blackbox:~# df -h -F btrfs
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdb              299G   56K  296G   1% /mnt/btrfs01
root@blackbox:~#

Create a new file (dd)

root@blackbox:~# dd if=/dev/zero of=/mnt/btrfs01/file.10G bs=1M count=$((10*1024))
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 176.188 s, 60.9 MB/s
root@blackbox:~#

Check how much space this file uses on the file system

root@blackbox:~# df -h -F btrfs
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdb              299G   21G  276G   7% /mnt/btrfs01
root@blackbox:~#

root@blackbox:~# btrfs-show
Label: btrfs01  uuid: d2b77569-a8be-4ec7-862a-d0fc1e6c8511
     Total devices 2 FS bytes used 10.01GB
     devid    1 size 149.01GB used 12.03GB path /dev/sdb
     devid    2 size 149.01GB used 12.01GB path /dev/sdc

Btrfs Btrfs v0.19
root@blackbox:~#

Get the usage explanation from btrfs tool

root@blackbox:~# btrfs filesystem df /mnt/btrfs01/
Data, RAID1: total=11.00GB, used=10.00GB
Data: total=8.00MB, used=0.00
System, RAID1: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=1.00GB, used=14.11MB
Metadata: total=8.00MB, used=0.00
root@blackbox:~#

Create a btrfs file system on Debian wheezy

By Ludovic Francois on Thursday, December 15 2011, 18:34 - unix

Debian version

ludo@blackbox:~ % cat /etc/debian_version          
wheezy/sid
ludo@blackbox:~ % uname -a                               
Linux blackbox 3.0.0-12-generic #20-Ubuntu SMP Fri Oct 7 14:50:42 UTC 2011 i686 athlon i386 GNU/Linux
ludo@blackbox:~ %

btrfs package install

root@blackbox:~# apt-get install btrfs-tools

Reinitialize all LUNs in use for this new file system

root@blackbox:~# dd if=/dev/zero of=/dev/sdb bs=1M count=512
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 9.07636 s, 59.2 MB/s
root@blackbox:~# dd if=/dev/zero of=/dev/sdc bs=1M count=512
512+0 records in
512+0 records out
536870912 bytes (537 MB) copied, 9.06802 s, 59.2 MB/s
root@blackbox:~#

Check if any btrfs file system are already present on the system

root@blackbox:~# btrfs-show
Btrfs Btrfs v0.19
root@blackbox:~#

Create btrfs file system (metadata and data replicated)

root@blackbox:~# mkfs.btrfs -m raid1 -d raid1 -L btrfs01 /dev/sdb /dev/sdc

WARNING! - Btrfs Btrfs v0.19 IS EXPERIMENTAL
WARNING! - see http://btrfs.wiki.kernel.org before using

adding device /dev/sdc id 2
fs created label btrfs01 on /dev/sdb
     nodesize 4096 leafsize 4096 sectorsize 4096 size 298.02GB
Btrfs Btrfs v0.19
root@blackbox:~#

mount btrfs01

root@blackbox:~# mkdir /mnt/btrfs01
root@blackbox:~# mount /dev/sdb /mnt/btrfs01/

check the file system is mounted (it shows up twice the capacity really available)

root@blackbox:~# df -h -F btrfs
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdb              299G   56K  296G   1% /mnt/btrfs01
root@blackbox:~#

make a test to understand how the data are stripped across the LUNs

root@blackbox:~# dd if=/dev/zero of=/mnt/btrfs01/file.10G bs=1M count=$((10*1024))
10240+0 records in
10240+0 records out
10737418240 bytes (11 GB) copied, 176.188 s, 60.9 MB/s
root@blackbox:~#

root@blackbox:~# df -h -F btrfs
Filesystem            Size  Used Avail Use% Mounted on
/dev/sdb              299G   21G  276G   7% /mnt/btrfs01
root@blackbox:~#

root@blackbox:~# btrfs-show
Label: btrfs01  uuid: d2b77569-a8be-4ec7-862a-d0fc1e6c8511
     Total devices 2 FS bytes used 10.01GB
     devid    1 size 149.01GB used 12.03GB path /dev/sdb
     devid    2 size 149.01GB used 12.01GB path /dev/sdc

Btrfs Btrfs v0.19
root@blackbox:~#

root@blackbox:~# btrfs filesystem df /mnt/btrfs01/
Data, RAID1: total=11.00GB, used=10.00GB
Data: total=8.00MB, used=0.00
System, RAID1: total=8.00MB, used=4.00KB
System: total=4.00MB, used=0.00
Metadata, RAID1: total=1.00GB, used=14.11MB
Metadata: total=8.00MB, used=0.00
root@blackbox:~#

Ludo's notes

Tag - file system