How to use hosts with no storage disks

Dmitry Tantsur dtantsur at
Fri Oct 15 17:13:08 UTC 2021


On Fri, Oct 15, 2021 at 7:10 PM James Penick <jpenick at> wrote:

> This is something we've talked about doing at Yahoo some day. There are
> three separate problems to solve:
> 1. Diskless booting the compute node off the network. Mechanically this is
> possible via a number of approaches. You'd have a ramdisk with the
> necessary components baked in, so once the ramdisk loaded you'd be in the
> OS. I'm not sure if this can be fully accomplished via Ironic as yet. I'd
> need to ask an Ironic expert to weigh in.


> 2. Configuration of the compute node. Either a CI job which is aware of
> the compute node coming up and pushing configuration via something like
> Ansible, or perhaps using cloud-init with the necessary pieces loaded into
> a config-drive image which is provided as a part of the boot process. If we
> can have Ironic manage diskless booting systems then this would be a solved
> problem with user data.
> 3. VM storage could either be "local" via a large ramdisk partition
> (assuming you have a sufficient quantity of ram in your compute nodes), an
> NFS share which is mounted to the compute node, or volume backed instances.
> We were investigating this earlier this year and got stuck on the third
> problem. Local storage via ramdisk isn't really an option for us, since we
> already pack our compute nodes with a lot of ram, and we need that memory
> for the instances. NFS has issues with security, since we don't want one
> giant volume exported to all compute nodes due to security concerns, and a
> per-compute node export would need to be orchestrated. Volume backed
> instances seemed ideal, however we ran into some issues there, which are
> partially related to the block storage product we use. I'm hopeful we'll
> get back to this next year, a class of instance flavors booted on diskless
> compute nodes would allow us to offer even more cost-effective options for
> our customers.
> -James
> On Fri, Oct 15, 2021 at 3:54 AM A Monster <amonster369 at> wrote:
>> In Openstack, is it possible to create compute nodes with no hard drives
>> and use PXE in order to boot the host's system and therefore launch
>> instances with no local drive which is needed to boot the VM's image.
>> If not, what's the minimum storage needed to be given to hosts in order
>> to get a fully functional system.

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