- Using VirtualBox:
- 1 Core
- 3G RAM
- 500G System Disk (VMDKVDI, Dynamically Allocated)
- Set network to "Attached to Bridged Adapter"
- clone the latest democontent image as dist-YYMMDD
- Install avalon-vm-1.0-1.noarch.rpm to install the firstboot changes and tools
- Binary Package: http://avalonmediasystem.org/downloads/avalon-vm-1.0-1.noarch.rpm
- Source Package: http://avalonmediasystem.org/downloads/avalon-vm-1.0-1.src.rpm
- Prepare the disk for compacting
deleted files still take up space on the disk image. Write a big zero file to clear out that unused data
dd if=/dev/zero of=/tmp/foo bs=1M count=8192 oflags=direct; rm /tmp/foo
- run /usr/share/avalon/dist-prep to prepare the machine for release
- clear the command line history (history -c)
- shutdown the VM
- Compact the disk image
On the host run:
VBoxManage modifyhd avalon-vm-disk-YYMMDD.vdi --compact
- Export the appliance
- use a 0.9 version OVA
- use a MANIFEST
- copy the OVA to the distribution point
Adding the demo batch increased the size of the VM download from 3.2G to 7.4G. Partially its because we've make derivatives and there's really new content on the VM. But for a bigger reason, any disk space that gets allocated is stored in the image file – the VM doesn't know what's being used and what isn't. Since we download a largish package, untar it, and create a bunch of temp files, the VM disk image has a bunch of unused (from the OS point of view) disk that it still has to keep track of. Future research should include how to 'unuse' the disk space.
"zerofree" should do the trick, when combined with vboxmanager modifyhd <name> --compact
Cleaning Unused Disk Space
VirtualBox's VBoxManager tool supports a compact option when modifying hard drives. Unfortunately it only supports VDI so I'm experimenting with using VDI instead of VMDK for the disk container format. For the purposes of the release, there should be no functional difference, except that VDI is less efficient than VMDK (on the Base OS install the VDI is 6% larger).
After a BaseOS install (as described above), the VDI disk image takes 4,304M of space. A df on the system shows that 3405M is used for data, so there is nearly 1G of space which is a combination of filesystem overhead, VM sparse disk overhead, and non-zero-unused data.
The first step is to see if the filesystem can be compacted using
VBoxManage modifyhd --compact avalon-vm-base-130419b.vdi
After a few minutes it comes back and shows that 4303M is being used – we saved 1M by running it. I'm not impressed.
I know that I downloaded about 200M worth of update packages. If the filesystem writes to the same places on the disk as it did before, a big dd should change that unused data to zeros:
dd if=/dev/zero of=/tmp/foo bs=10M count=1024; rm /tmp/foo
Afterward, the container was 4313M so the container grew by 10M – after writing 10G of zeros. One would assume that the original deleted data is now zeros and the extra size is overhead of mapping a bunch of empty blocks.
Compacting it gives us a new disk size: 4077M – we've saved 400M by writing a big bunch of zeros. Hooray!
I've written 4G of data to the image and it is currently 8176M on disk, even after erasing the files from the filesystem.
I've written 8G of zeros to the disk