Re: [gentoo-user] virtualbox in headless configuration broken after update: delayed echo [ RESOLVED, kinda ]

["J. Roeleveld" <joost@antarean.org>]

On Wednesday, June 17, 2020 7:42:30 AM CEST n952162 wrote:
> On 06/17/20 06:48, J. Roeleveld wrote:
> > On Tuesday, June 16, 2020 11:08:23 PM CEST n952162 wrote:
> >> On 06/16/20 22:36, J. Roeleveld wrote:

<snipped>

> > I have not come across MS HyperV outside of small businesses that need
> > some
> > local VMs. These companies tend to put all their infrastructure with one
> > of
> > the big cloud-VM providers (Like AWS, Azure, Googles,...)
> > 
> > --
> > Joost
> 
> Thank you for this excellent survey/summary.  It tells me that vbox is
> good for my current usages, but I should start exposing myself to Xen as
> a possible migration path.

I would actually suggest to read up on both Xen and KVM and try both on spare 
machines.
See which best fits your requirements and also see if the existing management 
tools actually do things in a way that you can work with.

My systems have evolved over the past 25-odd years and I started using Xen to 
reduce the amount of physical systems I had running. At the time, VMWare was 
expensive, KVM didn't exist yet and was missing some important features for a 
few years after it appeared (not sure if this exists yet, not found anything 
about it on KVM):
- limit memory footprint of host-VM during boot.
- Dedicate CPU-core(s) to the host

Limiting the memory size is important, because there are several parts of the 
kernel (and userspace) that base their memory-settings on this amount. This is 
really noticable when the host thinks it has 384GB available when 370GB is 
passed to VMs.

Dedicating CPU-cores exclusively to the host means the host will always have 
CPU-resources available. This is necessary because all the context-switching 
is handled by the host and if this stalls, the whole environment is impacted.

For a lab-system, I was also missing the ability to save the full state of a 
VM for a snapshot. All the howto's and guides I can find online only talk 
about making a snapshot of the disks. Not of the memory as well. Especially 
when used to Virtualbox, you will notice this issue. When only snapshotting 
the disk, your snapshot is basically the state of when you literally pulled 
the plug of your VM if you want to restore back to this.

For KVM, I have found a few hints that this was planned. But I have not found 
anything about this. Virt-manager does not (last time I looked) support Xen's 
functionality of storing the memory when creating snapshots either. Which is 
why I don't use that even for my lab/testing-server.

As for tips/tricks (below works for Xen, but should also work with KVM):

The way I create a new Gentoo-VM is simply to create a new block-device 
(Either LVM or ZFS), do all the initial steps in the chroot from the host and 
when it comes to the first-reboot, umount the filesystems, hook it up to a new 
VM and start that.

Because of this, I can update the host as follows:
- create new "partitions" for the host-system.
- Install the latest versions, migrate the config across
- reboot into the new host.

If all goes fine, I can clean up the "old" partitions and prepare them for 
next time. If there are issues, I have a working "old" version I can quickly 
revert to.

--
Joost