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Move information about image size limitations to known issues

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Signed-off-by: Jonathon Anderson <janderson@ciq.com>
This commit is contained in:
Jonathon Anderson
2025-01-19 14:13:13 -07:00
parent 1e6f52df4d
commit 65078525eb
2 changed files with 42 additions and 38 deletions
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38
userdocs/contents/images.rst
View File

@@ -396,44 +396,6 @@ openSUSE Leap image and import it to Warewulf:
# podman save localhost/leap-ww:latest -o ~/leap-ww.tar
# wwctl image import file://root/leap-ww.tar leap-ww
Image Size Considerations
=========================
Base compute node 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.
Duplicating an image
====================

42
userdocs/contents/known-issues.rst
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@@ -54,3 +54,45 @@ To resolve this, remove the sockets from the source directory.
This issue was fixed in an upstream library and `should be resolved in Warewulf
v4.6.0. <https://github.com/warewulf/warewulf/issues/892>`_
Image Size Considerations
=========================
Node images can grow quickly as packages and other files are added
to them. Even these larger images are often 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:
* Warewulf's :ref:`two-stage boot support <booting with dracut>` effectively
eliminates this problem by handling the bulk of the image management within
Linux. This feature is currently in preview, and is subject to change; but it
is likely to become the default boot method in a future release.
* 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.