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HP BIOS reserve 2 GB Memory for devices? DL585 G2

 
stalder
Occasional Visitor

HP BIOS reserve 2 GB Memory for devices? DL585 G2

We have an Issue open @ Red Hat that maybe is HP Hardware related instead.
We set the Systemmemory ( 64 GB are in the host ) in grub.conf as Kernelboot option to 10 GB, but when we start the OS uses only 8 GB.
According to RedHat it is "Feature" that the HP BIOS reserve 2 GB Memory for devices.

Questions:
- Is this normal? For what use the BIOS 2 GB Memory?
- what happens when we have only 4GB physical Memory? Do I have then only 2GB Memory left?

Extract from RedHat Engineering:
******************************************
Dear Mr.,

the memory map provided by the bios (e820) reserves a 2 gig memory hole for device memory:

BIOS-e820: 0000000000000000 - 000000000009f400 (usable)
BIOS-e820: 000000000009f400 - 00000000000a0000 (reserved)
BIOS-e820: 00000000000f0000 - 0000000000100000 (reserved)
BIOS-e820: 0000000000100000 - 000000007fe50000 (usable)
BIOS-e820: 000000007fe50000 - 000000007fe58000 (ACPI data)
BIOS-e820: 000000007fe58000 - 0000000080000000 (reserved) # 2gig hole start
BIOS-e820: 00000000fec00000 - 00000000fed00000 (reserved) #
BIOS-e820: 00000000fee00000 - 00000000fee10000 (reserved) #
BIOS-e820: 00000000ffc00000 - 0000000100000000 (reserved) # 2gig hole end
BIOS-e820: 0000000100000000 - 000000107ffff000 (usable)

As this is "reserved" the linux kernel cannot use it. I've also verified that with our HP Product TAM. Your system is fitted with a cciss raid controller:
08:00.0 RAID bus controller: Hewlett-Packard Company Smart Array Controller (rev 03) <> The amount of reserved memory is relatively big because the controller itself has plenty of RAM for caching.

Any hint would be very appreciated