** Package changed: linux (Ubuntu) => subiquity
** Also affects: ubuntu-z-systems
Importance: Undecided
Status: New
** Changed in: ubuntu-z-systems
Assignee: (unassigned) => Skipper Bug Screeners (skipper-screen-team)
** Changed in: ubuntu-z-systems
Importance: Undecided => Medium
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https://bugs.launchpad.net/bugs/2083843
Title:
[UBUNTU 24.04] Installer stalls when using HMC drive
Status in subiquity:
New
Status in Ubuntu on IBM z Systems:
New
Bug description:
=======================================
=== Reported by Peter Oberparleiter ===
=======================================
---Problem Description---
Ubuntu installations performed in IBM Z LPAR via an HMC drive block for a
prolonged time (multiple days), making this installation path unusable. The
problem exists from Ubuntu 20.04 up to 24.10beta.
Machine Type = s390/IBM Z
---boot type---
CDROM / ISO image
---Install repository type---
CDROM
---Point of failure---
The IBM Z Hardware Management Console (HMC) can provide non-networked,
in-band access to Linux installation media via its HMC drive function. This
function can be used to install Linux in environments where a local FTP server
for use as boot and initial installation source is unavailable. Unfortunately
access to this function is very slow, with response times up to seconds for
reading directories and transferring chunks of installer data.
Starting with Ubuntu 19.10, the casper installer component
automatically makes use of the HMC drive if it contains a valid Ubuntu
installation media [1]. Since Ubuntu 20.04, the Ubuntu installer
mounts file-system images contained on the media, and accesses files
from those images in place. The resulting random-access pattern to
media data in combination with HMC drive response times add up to the
observed prolonged wait times.
Some ideas how to resolve this problem:
1. Remove HMC drive support from casper.
This is not preferred since it would also remove the ability of users
to install Ubuntu in environments without FTP server.
2. Make HMC drive support in casper configurable.
This could be done e.g. by evaluating a new parameter passed to casper
via the kernel command line. To enable users to install with either
option without having to change ISO contents, multiple installer .ins
files would also need to be added to the installer media.
3. Make use of hcwdrv/hwcdrvfs caching options
hmcdrv module parameter 'cachesize=4194304' should be used to maximize
transfer chunk size. Also hmcdrvfs should be called with options '-o
kernel_cache -o entry_timeout=3600 -o attr_timeout=3600' to ensure
that directory and file data is cached longer.
4. Change casper to automatically copy all HMC drive contents to RAM-
disk and work with the RAM-disk copy instead.
Given the time it takes for a full copy, such a function would need to
provide regular ETA on the console to prevent users from aborting the
installation due to lack of feedback.
[1]
https://git.launchpad.net/ubuntu/+source/casper/commit/scripts/casper?id=810c74e4f2894
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