Editing VM vCPUs and RAM

Virtual machine hardware settings determine the amount of Metered RAM and vCPU capacity that the VM consumes—larger VMs consume more Metered RAM and vCPU capacity. For information about how Metered RAM and vCPU capacity are calculated, see How usage is calculated.

Instructions

To edit the VM vCPU and RAM settings

Make sure the VM is fully powered off (not running or suspended).
We recommend that before you make any hardware changes to your VM, that you create a template of it. If any problems occur, you can restore your VM from this template.
Navigate to the VM Settings > Hardware page.

Show me how
1. Navigate to the environment that contains the VM you want to edit.
2. Click (Settings).
  
  If the Settings button isn’t visible, you don’t have permission to edit the VM settings. Work with your instructor or Skytap administrator to edit these settings.
3. The VM Settings page displays. Click the Hardware tab.
Choose the number of vCPUs that the VM will use.

If an x86 VM is hardware version 10 or newer, click Advanced to see multi-core vCPU options. By default, Skytap configures 1 vCPU core per socket.
Notes
- The maximum number of vCPUs for a single VM varies, depending on region. For a list of regional capabilities, see Skytap service limits.
- If an x86 VM is hardware version 9 or earlier, you can upgrade the VM hardware version to make advanced vCPU configuration options available. For instructions, see Upgrading VM hardware versions.
- Only valid vCPU configuration core and socket combinations are displayed.
For Power VMs, set vCPU sharing mode to either Uncapped or Capped.
- Capped – The VM can never exceed the entitled capacity, determined by the vCPUs and RAM values for the VM.
- Uncapped – The VM will automatically use any excess processor resources available in the shared resource pool, in excess of the entitled capacity. This is the default setting.
CPU sharing mode helps control costs for applications that determine license cost, based on vCPU usage.
Next to Hardware RAM, enter the amount of RAM (in MiB) for the VM.
Notes
- The amount of RAM (in GiB) must be equal to or greater than the number of vCPUs.
- The maximum amount of RAM available for a single VM varies, depending on region.
- For x86 VMs – Increasing the amount of RAM, also increases the IOPS performance (up to 16 GiB of RAM).
- For Power A CPU architecture that supports IBM i, AIX, and Linux (on Power) in Skytap. VMs – Increasing RAM enables higher Entitled capacity (effectively increasing CPU performance). For specific details, see the CPU Entitled capacity lookup table below.
- For AIX VMs – The minimum supported RAM is 2048 MiB (2 GiB).
If you want to limit Entitled capacity for a Power VM to a value lower than that calculated by vCPUs and RAM, click and type the Entitled capacity value you want to use.
Click Save.

Additional information

Follow vendor recommendations for the operating system and the installed applications when setting the CPU and RAM values. Generally:
- Additional CPU cores permit more concurrent system and application processes, which improves system performance.
- Additional RAM allows more applications to be active and improves access speeds for data.
Some VMs may not support every configuration option that Skytap allows you to set. The guest OS type and hardware version number determine the amount of CPUs and RAM that a VM can use.

For example:
- Windows Server 2008 R2 Standard VMs support a maximum of 4 CPUs. If you select 8 CPUs, 4 of those CPUs are ignored by the guest OS.
- VM (x86 The most common CPU architecture. x86 CPUs support Windows and Linux VMs in Skytap. ) hardware versions 9 and earlier don’t support 12 CPUs or 256 GiB of RAM. For example, if you select 12 CPUs for a VM on hardware version 7, you may see an error message when the VM runs.

Entitled Capacity and CPW for Power VMs up to four CPUs

For Power VMs, set Entitled capacity (and approximate IBM i CPW) by changing the amount of RAM and the number of CPUs.

The table below was calculated with the following formulas:

EC=MIN(vcpu_count,FLOOR(MAX(GiB_ram/50,0.05)))
vcpu_limit=MIN(ROUNDUP(EC*20,0),16)
CPW=EC*10618 (approximate)

	CPU Cores
	1		2		3		4
RAM	EC	CPW	EC	CPW	EC	CPW	EC	CPW
1 GiB	0.05	530	---	---	---	---	---	---
2 GiB	0.05	530	---	---	---	---	---	---
3 GiB	0.06	743	0.06	743	---	---	---	---
4 GiB	0.08	1,061	0.08	1,061	---	---	---	---
5 GiB	0.10	1,274	0.10	1,274	0.10	1,274	---	---
6 GiB	0.12	1,592	0.12	1,592	0.12	1,592	---	---
7 GiB	0.14	1,805	0.14	1,805	0.14	1,805	0.14	1,805
8 GiB	0.16	2,123	0.16	2,123	0.16	2,123	0.16	2,123
16 GiB	0.32	4,247	0.32	4,247	0.32	4,247	0.32	4,247
32 GiB	0.80	8,494	0.64	8,494	0.64	8,494	0.64	8,494
48 GiB	0.96	10,618	0.96	12,741	0.96	12,741	0.96	12,741
64 GiB	1.00	10,618	1.28	16,988	1.28	16,988	1.28	16,988
128 GiB	1.00	10,618	2.00	21,236	2.56	31,854	2.56	33,977
256 GiB	1.00	10,618	2.00	21,236	3.00	31,854	4.00	42,472
512 GiB	1.00	10,618	2.00	21,236	3.00	31,854	4.00	42,472
CPW values are approximate.

Notes

This table provides some common RAM and CPU core combinations for Entitled capacity and CPW. You can choose other values for both RAM and CPUs—the updated Entitled capacity value displays in the Skytap interface.
The Entitled capacity (and approximate CPW) values in this table are guaranteed when the corresponding RAM and CPUs are configured for the VM.
Currently, a single IBM i VM supports a maximum of four CPU Cores (approximately 42,472 CPW).
If you change Entitled capacity for an active Power VM, it will display updated values but those values aren't applied to the VM until it's completely shut down, and then started again.

Entitled Capacity for AIX and Linux on Power VMs for more than four CPUs

For Power VMs, set Entitled capacity by changing the amount of RAM and the number of CPUs.