AIX 5.3 memory queries 3

[Midrange]

Hi there,

i have a new system P520 with os v5.3. we have ordered 4Gb of memory (8 x 512Mb). But when i chekced the amount installed (prtconf and lsattr command) i only got 3792Mb. I'm just confused since the required memory on P520 is in quad. then if i have problem with other memory then i should only get 2048Mb.

is there a new feature on V5.3 where in some of the memory were allocated or dedicated to other resources?

thanks.

 

[RMGBELGIUM]

this memory that is "lost" is used for the hypervisor( controls your LPARs ) of your machine.So it is correct that you're missing some of your ram when doing an lsattr -El mem0

rgds,

R.

 

[p5wizard]

Yes, phyp is *always* running, even if your machine is not LPARed or not even connected to an HMC. The FSP (service processor) on powering up, loads the phyp code from flash into main memory and then fires up the main processors, thereby using up some of your installed memory.



HTH,

p5wizard

 

[Midrange]

thanks. It's my first P5 server. I was surprised when i did not get the exact amount of memory.

so this feature only starts on P5 server? does it give any rule/computation how much memory will be consumed on the hypervisor?

thanks for both of you..you both deserve a star..

 

[Midrange]

Is there a way i can prove to the client that the machine have a 4Gb of memory aside from checking it physically? is there any command that will show that the other memory was used by the hypervisor or will give me a total of 4gb memory?

thanks

 

[oraytektips]

Yes, phyp is *always* running, even if your machine is not LPARed or not even connected to an HMC. The FSP (service processor) on powering up, loads the phyp code from flash into main memory and then fires up the main processors, thereby using up some of your installed memory.
HTH,
p5wizard

What is phyp,FSP and HTH
thank you

 

[p5wizard]

phyp = power hypervisor - machine code which distributes/dispatches hardware resources to the partition(s) which run the Operating System(s).

FSP = Flexible Service Processor - subsystem which controls the p5 hardware and to which an HMC can be connected.

HMC = Hardware Management Console - visualises the managed system(s) and provides a user interface for creating and controlling LPARs as well as a support interface (automatic call-home in case of problem).

LPAR = Logical PARtition: a collection of hardware resources (CPUs or timeslices thereof, memory, physical or virtual IO adapters) which can run an Operating System.
In case of p5 hardware, you can run AIX53, AIX52-04, RedHat, Suse, i5-OS, AIX-VIOS, Linux-VIOS on an LPAR - some limitations apply as to what type of partition can run what version of what Operating System.

Hope This Helps?

p5wizard

For more information, see the IBM and Redbooks websites.

 

[p5wizard]

To find out installed memory:

lscfg -vp |grep -p DIMM|egrep 'DIMM|Size'

Your machine may not look LPARed to you, but in fact it is running 1 partition which has all the CPUs, all the IO slots and *most* of the memory.

Some memory is set aside for phyp, for PFT (Page Frame Table - the partition needs to know where its memory is at, so it needs an addressing scheme for it - hence PFT) and for TCE - reserved memory to allow DMA transfers between IO adapters and system/partition memory. Also some memory will be left unused, because what's left over isn't enough to make up a memory block to be used by a partition. (Or because usable memory needs to start at a specific memory boundary I believe.)

In your case, up to 4GB installed, the default memory block size = 16MB. 237 blocks are usable LPAR memory: 237 * 16MB = 3792MB. 19 blocks (304MB) are used for phyp, PFT and TCE. Not a whole lot you can do about it.


HTH,

p5wizard

 

[dawaves]

p5wizard,

how did you know that 19 blocks were allocated to phyp, PFT and TCE? What is the ratio between real memory and memory used by hypervisor, etc?

I have a similar issue w/ a newly ordered p5 510. I had 2GB of memory installed but it only shows 1856 of real memory. Until this topic, I thought my memory was just bad, lol.


Thanks!

 

[p5wizard]

How did I know? Arithmetic...

4GB in 16MB blocks = 256 blocks
system shows 3792 MB = 237 blocks
256 - 237 = 19
19 blocks are in use by the server for all kinds of stuff
phyp, TCE, PFTs
237 blocks are allocated as real mem to the one and only partition.

actually it might be a bit less than 19 blocks in use, there may also be a few blocks left unused...

Actually there's a LPAR validation tool available on the IBM website which does an estimation of the used phyp memory if you want to verify.


HTH,

p5wizard

 

[dawaves]

p5wizard,

Thanks!

How do I become a p5wizard?

 

[p5wizard]

Practice makes perfect.


HTH,

p5wizard