Before you install a hypervisor on a new Dell PowerEdge server, spend ten minutes in System BIOS. A few settings decide whether VMs can use hardware virtualization, whether SR-IOV network cards can present virtual functions, and how the CPUs trade power for performance. This guide explains where each setting is and what Dell documents for it, using the PowerEdge R750 BIOS and UEFI Reference Guide (15G) and the R760 Installation and Service Manual (16G). Other models use similar names, but always check the manual for your exact model.
Before you start
- Find the BIOS reference for your model on the Dell support site. For 15G models Dell publishes a separate BIOS and UEFI Reference Guide; for 16G models such as the R760 the BIOS options are in the Installation and Service Manual.
- Plan a maintenance window: BIOS changes need a restart.
- Write down or export the current values before you change anything, so you can go back.
- Update the BIOS to a current version first; option lists change between BIOS releases.
Where the settings are
Dell documents two ways to reach the BIOS settings:
- Locally or through the virtual console: power on, press F2 and open System Setup Main Menu > System BIOS. If the OS starts to load before you press F2, let it finish booting, then restart and try again.
- From iDRAC: on the iDRAC dashboard, click Configurations > BIOS Settings.
In System Setup, press Esc to go back to the System BIOS screen, press Esc again and confirm when you are asked to save the changes. For how iDRAC applies pending changes, see the iDRAC user guide and our iDRAC9 job queue guide.
Step 1 — Processor Settings: virtualization and threads
Path: System BIOS > Processor Settings. The options that matter most for virtualization:
| Option | Default (R750 and R760) | What Dell says |
|---|---|---|
| Virtualization Technology | Enabled | Enables or disables virtualization technology for the processor. Hypervisors need it on. |
| Logical Processor | Enabled | Each core supports up to two logical processors; Disabled shows only one per core. |
| x2APIC Mode | Enabled | Not switchable in some high core-count configurations; see the note for your model. |
| Sub NUMA Cluster | Disabled | Enables or disables Sub NUMA Clustering. Leave it at the default unless your workload vendor recommends a change. |
| Kernel DMA Protection | Disabled (R760) | When enabled, the BIOS and OS protect against DMA from capable peripherals using virtualization technology. |
The R760 manual also lists CPU Physical Address Limit (Enabled by default), which limits the CPU physical address to 46 bits to support older Hyper-V and, if enabled, disables TME-MT. Leave it at the default unless your hypervisor vendor tells you otherwise.
Step 2 — Integrated Devices: SR-IOV Global Enable
Path: System BIOS > Integrated Devices > SR-IOV Global Enable. It enables or disables the BIOS configuration of Single Root I/O Virtualization (SR-IOV) devices and is Disabled by default on both the R750 and the R760. Turn it on only if you plan to use SR-IOV virtual functions on a network or other adapter, for example for VM passthrough of NIC virtual functions. The adapter and its driver must also support SR-IOV; some adapters have their own SR-IOV setting under Device Settings, so check the adapter's user guide.
Step 3 — System Profile Settings: power versus performance
Path: System BIOS > System Profile Settings > System Profile. The profile sets a group of CPU and memory power options at once.
| Profile | Notes from Dell's documentation |
|---|---|
| Performance Per Watt (DAPC) | The default. CPU Power Management is then System DBPM (DAPC). |
| Performance Per Watt (OS) | As the name says, a performance-per-watt profile with the OS taking part in power management (CPU Power Management offers an OS DBPM value). |
| Performance | Sets the profile options for performance rather than power saving; review the values it sets. |
| Workstation Performance | Listed as an option on the R750 and R760. |
| Custom | The only profile where you can change the individual options yourself. |
When you choose any profile other than Custom, the BIOS sets the remaining options for you; you can change them only in Custom. Useful options shown on this screen:
- CPU Power Management — System DBPM (DAPC), Maximum Performance or OS DBPM.
- Memory Frequency — Maximum Performance (default), Maximum Reliability or a specific speed.
- Turbo Boost and C1E — both Enabled by default.
- C States — Enabled by default. Dell notes that C-states save power but may increase memory latency and frequency jitter.
- Workload Profile (R760) — lets you name the target workload to tune performance; Not Configured by default.
How to choose: keep the default DAPC profile for general workloads where power use matters. Choose Performance for latency-sensitive workloads (databases, real-time apps) after checking power and cooling capacity. Choose Performance Per Watt (OS) if you want the hypervisor's own power policy to control CPU power states. After selecting a profile, review the read-only values it sets so you know what changed. The R760 manual also notes that Dell Controlled Turbo should be enabled only when System Profile is Performance or Custom and CPU Power Management is Performance.
Step 4 — Memory Settings
Path: System BIOS > Memory Settings.
- Memory Operating Mode — Optimizer Mode is the default on the R750. The R760 manual describes Optimizer Mode (DRAM controllers work independently for optimised performance), Dell Fault Resilient Mode (FRM) and Dell NUMA Fault Resilient Mode, which reserve a percentage of memory as a fault-resilient zone for select hypervisors. The percentage is set in Fault Resilient Mode Memory Size[%]. The mode is active only if a valid memory configuration is detected.
- Node Interleaving — Disabled by default, which means the system supports NUMA. Enabled interleaves memory across nodes when the memory configuration is symmetric. Hypervisors are NUMA-aware, so leave it Disabled unless your software vendor says otherwise.
- System Memory Size and System Memory Speed — read-only; use them to confirm that all installed memory is seen. See PowerEdge memory population rules.
Step 5 — Boot Settings: UEFI
Path: System BIOS > Boot Settings > Boot Mode. UEFI is the default. Dell lists its benefits as support for partitions larger than 2 TB, Secure Boot and faster boot, and states that you must use UEFI boot mode to boot from NVMe drives. BIOS (legacy) mode is kept only for older operating systems.
Warning: Dell cautions that switching the boot mode may prevent the system from booting if the OS was installed in the other mode. Choose the boot mode before you install the OS and do not change it on a running system. If you must, have a tested backup and recovery media ready. Back up first.
Frequently asked questions
Is Virtualization Technology enabled from the factory?
The R750 reference guide and the R760 manual both list Virtualization Technology as Enabled by default. Check it anyway if the hypervisor reports that hardware virtualization is unavailable.
Why can't I change C States or Turbo Boost?
Those options are set by the System Profile. Dell's documentation states that you can change them only when System Profile is set to Custom.
Checklist
- BIOS updated and the manual for your exact model at hand.
- Current settings recorded before changes.
- Virtualization Technology and Logical Processor Enabled.
- SR-IOV Global Enable turned on only if SR-IOV adapters will be used.
- System Profile chosen on purpose (DAPC, OS, Performance or Custom) and resulting values reviewed.
- Memory Operating Mode and Node Interleaving left at defaults unless a vendor requires otherwise; full memory size visible.
- Boot Mode set to UEFI before OS installation.
- Changes saved and the server restarted in a maintenance window.
Skyline can supply, configure and maintain Dell, HPE and Huawei servers under an annual maintenance contract (AMC). Contact us.
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