Originally posted by: SystemAdmin

Hi all,

My customer has a new 9111-510 (p510) machine with 4 RAM modules (256Mb each). When they plug 2 RAMs, the machine reports only 384MB, so we lost 128MB of RAM here. When they plug all the 4 RAMs, the machine reports 880Mb, so we lost 144Mb (128 + 16) of RAM here?!

I test all the RAMs and they all are in good state, so where is the rest of RAM capacity?

I heard about a new technology in p5 system that will use RAM but don't know the name, I wonder if this case is that.

Anyone can explain for me? My customer need proof otherwise they will keep asking me for new RAM :(

Thank you.

Originally posted by: SystemAdmin

You did not say whether you were using partitioning or not, but I assume that you are not and that you are seeing these numbers from inside of your AIX. The key is that with POWER5, even the full machine partition runs under the hyperviosr. This means that you will not see the hypervisor memory from inside the AIX partition. If you have an HMC, you can see how much memory is used by different LPARs and how much is used by the system resources such as the hypervisor, TCE (Translation Control Elements), and by the partition page table. The hypervisor will not always be the same, but takes about 256 MB. The partition page table space is 1/64 of the total memory for each LPAR rounded up to the next power of 2. This is then packed into LMB (Logical Memory Blocks) which are different based on the total memory size in the system.

Hope this helps you start to understand this.

Originally posted by: SystemAdmin

In this case, it looks like the 128 is likely hypervisor and the small amount of page table space, when you add more memory, the partition page table space increases.

Originally posted by: SystemAdmin

Thank you CompuChem,

Yes, I don'n use LPAR here and have no HMC, I saw the RAM capacity showing by AIX command.
But for some other p5 machines, like p550Q or p570, I still see the full RAM capacity? (7990Mb or smthing like that, that means customer have 8G RAM). Are those p5 machines (p550Q, p570) using hypervisor or not? Can we disable this technology? :)

So far, do you have any official document talking about hypervisor? I perhaps need it to explain for my customer.
Thank you in advance.

Originally posted by: SystemAdmin

All power5 systems will always have the hypervisor running. There will always be a hypervisor memory expense. This just shows up as a larger percentage for small memory systems. There is no way to turn this off. On Power4, you could run full machine partition and it did not use the hypervisor.