Red Hat Bugzilla – Bug 233537
Lack of x86 kernel-PAE Support for >16GB in RHEL5
Last modified: 2016-04-18 05:46:16 EDT
Description of problem:
RHEL 4 supports up to 64GB using the hugemem kernel.
RHEL 5 does not ship the hugemem kernel and officially restricts support to
systems of 16GB or less. However, kernel-PAE will install and run systems up to
64GB with no warning message that this is an invalid consiguration.
Engineering's position is that customers wanting to run larger systems should
migrate to x86_64 architecture.
Though there are not a large number of x86 systems, the ones that do exist
typically are from large customers and we are inhibiting them from migrating to
RHEL5. Many can't easily migrate their applications to run on 64 bit or they
don't own the proprietary application software.
The intent of this bug is to resolve the migration roadblock that customers
running x86 16-64GB systems will experience if they can not migrate their
applications to 64 bit. For them, this is a regression from RHEL4.
From Amit at Dell:
Attaching the sos report from a PE6950 with 64 GB RAM that is loaded
with RHEL5 32-bit. kernel-PAE sees all 64GB.
Created attachment 150707 [details]
sos -- Kernel-PAE.tar.bz2
This bugzilla has Keywords: Regression.
Since no regressions are allowed between releases,
it is also being proposed as a blocker for this release.
Please resolve ASAP.
The problem here is that there is no warning that the customer is running an
invalid configuration in RHEL5.
The 2.6.18 kernel will boot and appears to run with memory as large as 64GB. In
RHEL3 and RHEL44, you could boot a 24GB kernel but it would likely behave poorly
and the kernel would not even boot at 32GB.
The first time the customer is aware that a valid RHEL4 configuration (albeit
using the hugemem kernel) is now invalid in RHEL5 is when he/she calls Support
and they relate that >16GB is not supported in 32 bit mode on RHEL5.
It is also not clear that all applications can run or are certified in 32 bit
mode on a 64 bit OS for RHEL5. This could be a significant customer migration
problem to RHEL5.
Development Management has reviewed and declined this request. You may appeal
this decision by reopening this request.