On Thu, Apr 06, 2017 at 02:03:55PM +0200, Laurentiu Pancescu wrote:
Hi there,
I created the first experimental Vagrant images for Hyper-V on March 14, after the CBS upgrade. They seem to be functional, but they generate a lot of disk I/O during "vagrant up", according to Thomas and Michael. I think we end up with 40GB files as disk images - this is the maximum size of the virtual hard drives we create, but most of that is empty. I compared the contents of our box file to the one from kozo/centos-7, which is produced natively using Packer and Hyper-V: our image contains a real 40GB disk image, while the kozo image only has a 2.1GB image.
Image Factory converts the KVM .qcow2 image to a .vhd by calling "qemu-img convert -O vpc <source> <destination>". This produces a 40GB sparse file taking just 1.1GB of space (both with the fixed and dynamic subformats). The problem occurs while packing the sparse image into the .box file: Python's tarfile module only has read-only support for sparse files (a GNU tar extension) - even in Python 3, so the archive ends up with a regular 40GB file.
Creating 40GB sparse files seems to be specific to qemu-img: "VBoxManage convertmedium disk box.vmdk box.vhd" produces a 1.1GB regular file (VirtualBox' convert tool doesn't seem to support QCOW2, so I had to first convert the QCOW2 image to VMDK).
We should probably either:
- call GNU tar from Image Factory to preserve the sparseness of our image
files (and hope that Windows handles them properly)
- use VBoxManage to convert to .vhd (VirtualBox is not in our repos, but
Oracle offers a .rpm for EL7 systems).
In the mean time, we will probably release v1703 without Hyper-V support, since CentOS Linux 6.9 was already released.
Maybe you can post-process the large .vhd file with "virt-sparsify"? I do not know if it would recognize the format, but it is worth to try it. Otherwise it should be possible to "punch holes" in the large .vhd file with a little program that calls fallocate(2) on zero-filled areas.
HTH, Niels
Best regards, Laurențiu
[vagrant@localhost ~]$ tar -tvzf c7.box # that's ours drwxr-xr-x root/root 0 2017-03-14 11:23 Virtual Machines/ -rw-r--r-- root/root 39100 2017-03-14 11:23 Virtual Machines/vm.XML -rw-r--r-- root/root 114 2017-03-14 11:23 Vagrantfile drwxr-xr-x root/root 0 2017-03-14 11:22 Virtual Hard Disks/ -rwxr-xr-x root/root 42949672960 2017-03-14 11:23 Virtual Hard Disks/disk.vhd -rw-r--r-- root/root 22 2017-03-14 11:23 metadata.json
[vagrant@localhost ~]$ unzip -l hyperv.box # kozo/centos-7 Archive: hyperv.box.zip Length Date Time Name
36898 02-25-2017 13:05 VirtualMachines/1BF518E8-0055-4ABF-8750-E1D703B23A47.vmcx 61440 02-25-2017 13:05 Virtual Machines/1BF518E8-0055-4ABF-8750-E1D703B23A47.VMRS 64 02-25-2017 12:47 metadata.json 2185232384 02-25-2017 13:05 Virtual Hard Disks/CentOS7.vhdx
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