Using lvm thin provisioning

gistfile1.sh

# Using lvm thin provisioning, per https://github.com/lxc/lxc/pull/67

# First we create a volume group to hold the thin pool

$ sudo vgcreate lxc /dev/sde3

# Then create a thin-pool named 'tp' within that volume group

$ sudo lvcreate -l 90%VG --type thin-pool --thinpool tp lxc

# Now, create a 8GB container with lvm as the backing store, allocated from the thin-pool above

$ sudo lxc-create -n precise-thin --fssize=8G -B lvm --thinpool tp -t ubuntu-cloud -- -r precise

# We can see below that this only allocated 0.64% of the thin-pool, or about 0.97GB here, and the same amount within the 'precise-thin' LV.

$ sudo lvs
  LV           VG   Attr      LSize   Pool Origin Data%  Move Log Copy%  Convert
  precise-thin lxc  Vwi-a-tz-   7.81g tp           12.56                        
  tp           lxc  twi-a-tz- 152.93g               0.64          

# Finally, we clone the original container. It will default to snapshotting the original LV using the same thin-pool.

$ sudo lxc-clone -s precise-thin precise-copy

# The total amount of data allocated in the thin-pool is pretty much the same.

$ sudo lvs
  LV           VG   Attr      LSize   Pool Origin       Data%  Move Log Copy%  Convert
  precise-copy lxc  Vwi-a-tz-   7.81g tp   precise-thin  12.59                        
  precise-thin lxc  Vwi-a-tz-   7.81g tp                 12.56                        
  tp           lxc  twi-a-tz- 152.93g                     0.64  

# Since I have a slightly old ubuntu-cloud image, let's run apt-get upgrade on one of the containers. The thin-pool usage is around 1.6GB now.

$ sudo lvs
  LV           VG   Attr      LSize   Pool Origin       Data%  Move Log Copy%  Convert
  precise-copy lxc  Vwi-aotz-   7.81g tp   precise-thin  17.63                        
  precise-thin lxc  Vwi-a-tz-   7.81g tp                 12.56                        
  tp           lxc  twi-a-tz- 152.93g                     1.09                        

# And if we do it again on the other container, we're now up to 2GB

$ sudo lvs
  LV           VG   Attr      LSize   Pool Origin       Data%  Move Log Copy%  Convert
  precise-copy lxc  Vwi-aotz-   7.81g tp   precise-thin  17.63                        
  precise-thin lxc  Vwi-aotz-   7.81g tp                 17.19                        
  tp           lxc  twi-a-tz- 152.93g                     1.33  

# The best savings would be from keeping a fresh base image available for cloning, since in this case just the upgrade added ~400MB.