Why is docker image eating up my disk space that is not used by docker

Hi, I have setup docker and I have used completely different block device to store docker’s system data:

[root@blink1 /]# cat /etc/sysconfig/docker
# /etc/sysconfig/docker

other_args="-H tcp:// -H unix:///var/run/docker.sock -g /disk1/docker"

Note that /disk/1 is using a completely different hard drive /dev/xvdi

Filesystem      Size  Used Avail Use% Mounted on
/dev/xvda1      7.8G  5.1G  2.6G  67% /
devtmpfs        1.9G  108K  1.9G   1% /dev
tmpfs           1.9G     0  1.9G   0% /dev/shm
/dev/xvdi        20G  5.3G   15G  27% /disk1
/dev/dm-1       9.8G  1.7G  7.6G  18% /disk1/docker/devicemapper/mnt/bb6c540bae25aaf01aedf56ff61ffed8c6ae41aa9bd06122d440c6053e3486bf
/dev/dm-2       9.8G  1.7G  7.7G  18% /disk1/docker/devicemapper/mnt/c85f756c59a5e1d260c3cdb473f3f4d9e55ac568967abe190eeaf9c4087afeac

The problem is that when I continue download docker images and run docker containers, it seems that the other hard drive /dev/xvda1 is also used up.

I can verify this problem by remove some docker images. After I removed some docker images, /dev/xvda1 has some more extra space now.

Am I missing something?

My docker version:

[root@blink1 /]# docker info
Containers: 2
Images: 42
Storage Driver: devicemapper
 Pool Name: docker-202:1-275421-pool
 Pool Blocksize: 64 Kb
 Data file: /disk1/docker/devicemapper/devicemapper/data
 Metadata file: /disk1/docker/devicemapper/devicemapper/metadata
 Data Space Used: 3054.4 Mb
 Data Space Total: 102400.0 Mb
 Metadata Space Used: 4.7 Mb
 Metadata Space Total: 2048.0 Mb
Execution Driver: native-0.2
Kernel Version: 3.14.20-20.44.amzn1.x86_64
Operating System: Amazon Linux AMI 2014.09

mmm, this might be a good one to make a github issue for - there is some focus being put on devicemapper issues at the moment .