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Add a section on container sizes and workarounds

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Signed-off-by: Jonathon Anderson <janderson@ciq.co>
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Jonathon Anderson
2023-04-21 14:29:39 -06:00
parent d9782688b1
commit d0a0feff15
1 changed files with 38 additions and 0 deletions
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userdocs/contents/containers.rst
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@@ -259,3 +259,41 @@ openSUSE Leap container and import it to Warewulf:
# podman build -f containers/Docker/openSUSE/Containerfile --tag leap-ww # podman build -f containers/Docker/openSUSE/Containerfile --tag leap-ww
# podman save localhost/leap-ww:latest -o ~/leap-ww.tar # podman save localhost/leap-ww:latest -o ~/leap-ww.tar
# wwctl container import file://root/leap-ww.tar leap-ww # wwctl container import file://root/leap-ww.tar leap-ww
Container Size Considerations
=============================
Base compute node container images start quite small (a few hundred
megabytes), but can grow quickly as packages and other files are added
to them. Even these larger images are typically not an issue in modern
environments; but some architectural limits exist that can impede the
use of images larger than a few gigabytes. Workarounds exist for these
issues in most circumstances:
* Systems booting in legacy / BIOS mode, being a 32-bit environment,
cannot boot an image that requires more than 4GB to decompress. This
means that the compressed image and the decompressed image together
must be < 4GB. This is typically reported by the system as "No space
left on device (https://ipxe.org/34182006)."
The best work-around for this limitation is to switch to UEFI. UEFI
is 64-bit and should support booting significantly larger images,
though sometimes system-specific implementation details have led to
artificial limitations on image size.
* The Linux kernel itself can only decompress an image up to 4GB due
to the use of 32-bit integers in critical sections of the kernel
initrd decompression code.
The best work-around for this limitation is to use an iPXE with
support for `imgextract <https://ipxe.org/cmd/imgextract>`_. This
allows iPXE to decompress the image rather than the kernel.
* Some BIOS / firmware retain a "memory hole" feature for legacy
devices, e.g., reserving a 1MB block of memory at the 15MB-16MB
address range. this feature can interfere with booting stateless
node images.
If you are still getting "Not enough memory" or "No space left on
device" errors, try disabling any "memory hole" features or updating
your system BIOS or firmware.