change required minimum disk size from 120GB to 100GB #35793
Comments
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To me a bottom line here is "what do our default e2e tests require". Hmm actually do we have any e2e tests that cover IBM Cloud VPC installs? I'm not seeing them offhand in release controller. |
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related openshift/installer#5169 |
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From background conversations, it seems like this original decision was partly based on the fact that iops and storage scale together in public clouds. I think we should
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I think Azure is strictest about that, but they're pretty decoupled in AWS for example. But completely agree about IOPS being quite important here versus disk size. |
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Agreed here. 100GB fine as a minimum (assuming our IOPS and latency requirements are met). 120GB was what we increased it to in our initial releases on AWS with gp2 to satisfy our IOPS needs to pass the e2e CI suites reliably. |
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I agree as well!!!!!! (From IBM Cloud side) |
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Agree. |
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@relyt0925 Please consider these approval comments as approval for this change and to let you run within the OCP requirements. I'll work on getting this drafted and merged, but that shouldn't stop you from doing what you need. |
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Comment from Z and LinuxONE side, I agree in lower the boundary and appreciate, but we need the same change for all Z and LinuxONE configurations including zVM setup. |
I was looking at this issue: openshift/openshift-docs#35793 Which then led me to wonder exactly what the defaults are per platform for disk sizes. And then I stumbled into this 120 vs 128 thing that as best I can tell from the git history is mostly an accident. If someone happens to know differently (e.g. can/should we unify on 120 or 128?) then that'd be good. In the meantime, an additional benefit here is that if one does e.g. `git grep -i volume.*size` these constants will turn up. It took me a little while to figure out how to backtrack from the Terraform code to this. (The lines here only contained `Size` which is too generic to grep)
Which section(s) is the issue in?
https://docs.openshift.com/container-platform/4.8/installing/installing_bare_metal/installing-bare-metal.html#minimum-resource-requirements_installing-bare-metal
https://docs.openshift.com/container-platform/4.8/installing/installing_ibm_z/installing-ibm-z-kvm.html#minimum-resource-requirements_installing-ibm-z-kvm
https://github.com/openshift/openshift-docs/blob/main/modules/installation-requirements-user-infra.adoc
https://github.com/openshift/openshift-docs/blob/main/modules/installation-requirements-user-infra-ibm-z-kvm.adoc
What needs fixing?
The minimum required disk size is stated as 120GB but this is too large. Anecdotal evidence has shown that 100GB is a more appropriate minimum.
Discussion
This change was spurred on by work being done for IBM Cloud. The RHCOS disk image for IBM Cloud currently has the
virtual sizehard coded to 100GB, as recommended by the IBM Cloud documentation. See the original PR for the change for context - coreos/coreos-assembler#2041 (comment)However, the folks working on IBM Cloud support for all of OCP noted that our documentation states that 120GB is the minimum.
An issue was opened upstream in the Fedora CoreOS tracker requesting that the disk size was increased. Since FCOS is the upstream to RHCOS, this change would affect both projects.
coreos/fedora-coreos-tracker#931
During the discussion on that ticket (and in internal Slack discussions), the best path forward appeared to be an update to the OCP docs. This is because the IBM Cloud does not support resizing the disk in the cloud and it is suspected that is not possible for the installer to resize the disk before the upload to the cloud.
Alternatively, if the broad minimum cannot be changed, it has been suggested that we change the docs to note that the 100GB minimum would apply to IBM Cloud.
This ticket has been opened to allow for discussion on the proposed change to our documented minimums and any implications that may have.
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