On 05/22/2018 05:51 PM, [email protected] wrote:
I want to do the following.
1. Create an HVM Qube. This Qube contains a clean install of an OS such as
Windows 8 or Arch.
2. Clone the Qube from #1. The files that make up this Qube should just contain
the delta from the parent Qube. Writes are made to the child Qube; reads go to
the child Qube (if the data being read was written previously) or to the parent
Qube if not (in other words, copy-on-write.) I want to install applications in
this Qube, so changes should persist.
Hyper-V does this with differencing disks (see
https://technet.microsoft.com/en-us/library/cc720381.aspx.)
It looks like Xen does this also, with fast cloning (see
https://docs.citrix.com/en-us/xencenter/6-2/xs-xc-vms/xs-xc-vms-copy.html.)
My question is, can this be done in Qubes? From searching the Web and the docs,
it looks like not, but I thought I'd see if I've overlooked anything.
One way would be to have a TemplateVM and a TemplateBasedVM, but have changes
to the TemplateBasedVM (outside of /home) be persistent. I don't know if Qubes
allows that.
One possible way (I think) would be to use Btrfs as the dom0 file system, but I
don't know if that's allowed either.
Otherwise, I'll have to create the parent Qube and then clone it with
qvm-clone, but it looks like that creates a full copy, which I'd rather avoid
if possible due to the disk space consumption.
By default, the Qubes 4.0 volume manager will always create COW (not
full) clones. If you choose btrfs instead, the effect will also be the same.
One Qubes 3.2, you have to choose btrfs (or prepare a pool with a
similar filesystem having COW reflinks) for this type of cloning to work.
Keep in mind that (as with Hyper-V) these block level differencing
volumes will diverge increasingly over time as updates are applied. That
means the initial space savings will begin to shrink. I don't know if
Hyper-V has a solution to this, but on Linux one way to help prevent
divergence is deduplication (such as in btrfs).
Overall, these cloning options (using LVM or btrfs) should work more
smoothly than Hyper-V storage. Note the warnings re: volume spoilage on
the Microsoft page don't apply to Qubes; you still have to update each
cloned OS, but there is no need for you to keep track of volumes to
avoid spoilage.
--
Chris Laprise, [email protected]
https://github.com/tasket
https://twitter.com/ttaskett
PGP: BEE2 20C5 356E 764A 73EB 4AB3 1DC4 D106 F07F 1886
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