Question

How does Prism display memory installed?

  • 24 August 2021
  • 2 replies
  • 84 views

Hi, we installed 32 * 12 = 384 GB of memory.
However, in Prism, it is displayed as 377gib.


384 GB to GiB Conversion =357gib.
I want to know why prism displays 377gib.


If anyone knows, please reply.
Thx


2 replies

Userlevel 1
Badge +1

I think the missing goes to the needs of the virtualizer AHV (centos), which is below the level

 

Userlevel 3
Badge +5

The host memory capacity displayed by Prism is the memTotal value which can be used by the AHV hypervisor. This value can be obtained by looking into the MemTotal value listed in the cat /proc/meminfo command output on the AHV host:

cat /proc/meminfo | grep MemTotal

The same memory capacity value can also be found using free -g command output (shows memory values in GiB) on the AHV host and looking into the Mem Total value in it.

free -g
  • Since Mem Total value is directly shown in GiB in the above output, you don’t need to convert it to GiB again - this value should match to what is being seen in Prism.  

As per the proc kernel doc, there is a discrepancy between the MemTotal values seen in cat /proc/meminfo or free command outputs versus to actual physical memory installed on the Hardware node is because MemTotal shows the Total usable ram which is Physical ram minus a few reserved bits and the kernel binary code. 

Regarding the actual Physical memory DIMM value calculation, RAM Memory capacity is always measured in powers of two (1 KiB equals 1024 B), so 32 GB actually means 32 GiB. It is typically stated as GB because it is easier to understand as compared to GiB. Hence, based on this calculation, you actually have 32*12 = 384 GiB of physical RAM available on the node.

Now from this 384 GiB of physical RAM, 377.5 GiB of RAM is available for use by the AHV hypervisor (which is what should come up in cat /proc/meminfo or free command outputs as well) and remaining RAM is used by some reserved bits and kernel binary code. 

 

I hope this helps to clear the discrepancy between host memory capacity values seen in Prism web console versus to the actual physical memory installed in the node. 

 

 

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