What is a ESXi host?

An ESXi host is a physical server that runs VMware’s bare-metal hypervisor, ESXi, to virtualize compute, storage, and networking resources for virtual machines. As a type of Type-1 or bare-metal hypervisor, ESXi installs directly onto server hardware and partitions it into multiple virtual machines that can run operating systems and applications independently.

What is a ESXi host?
Some key capabilities and characteristics of an ESXi host include:

  • Enables server virtualization for workload consolidation and resource optimization
  • Supports advanced virtualization features like vMotion, High Availability, Distributed Resource Scheduler, Storage vMotion and more
  • Typically runs on server-grade hardware from vendors like Dell, HPE or Lenovo for reliability and performance
  • Requires 64-bit x86 servers meeting exact hardware compatibility requirements
  • Functions as a standalone host or clusters into a vSphere environment centrally managed by vCenter Server
  • Divides physical resources of the server to securely and efficiently power virtual machines
  • Hosts the VMkernel hypervisor operating system optimized for speed and small footprint
  • Leverages VMware Forged certifications for server hardware, firmware and drivers for maximum compatibility

Understanding ESXi host capabilities and management best practices is key for organizations utilizing VMware infrastructure for production workloads at scale.

Hardware requirements and compatability considerations

As a bare metal hypervisor installed directly on server hardware, an ESXi host has strict hardware compatibility requirements to function properly. VMware maintains an Hardware Compatibility List (HCL) documenting certified server models, components and drivers that are rigorously validated for vSphere environments.

Some key hardware compatibility considerations for ESXi hosts include:

Supported server platforms

VMware only supports ESXi installation on enterprise-grade server hardware meeting baseline reliability, security and performance standards. Supported platforms include:

  • Dell PowerEdge
  • HPE ProLiant
  • Lenovo ThinkSystem
  • Cisco UCS
  • Supermicro
  • And other x86 servers

CPU compatibility

ESXi runs on servers with 64-bit x86 Intel and AMD processors. Specific processor families, stepping levels, features sets and instruction sets must be certified for use. Multi-CPU systems are also supported to distribute workload demands.

Memory requirements

The host should have at least 8GB of physical RAM, but 32GB or more is recommended for production workloads. Advanced memory management features like page sharing, memory ballooning and compression operate most efficiently with ample host RAM.

Storage and RAID configuration

Fast and reliable storage with sufficient capacity for virtual machine files is mandatory. Most hosts leverage RAID configurations combining multiple disks into logical volumes for performance, fault tolerance and automated failover in case of disk failure.

Networking and I/O controllers

The NICs, HBAs, RAID and management controllers enable the host to connect with networks, shared storage and infrastructure management software like vCenter Server. Precision timed hardware and drivers certified for high-speed communication are vital.

Closely matching the HCL guidelines for processor family, drivers, firmware, management controllers and other components ensures maximum stability and supportability of the ESXi host.

ESXi host installation process

Transforming physical ‘bare metal’ server hardware into an ESXi host ready to host virtual machines involves installing the ESXi hypervisor to the server and customizing the environment.

Key steps for installing ESXi include:

  1. Check hardware compatibility on VMware HCL
  2. Update server firmware, BIOS settings and drivers
  3. Secure approved OS installation files from VMware
  4. Boot the server to the ESXi installer CD image/USB flash drive
  5. Select the storage disk target for installation
  6. Accept VMware End User License Agreement
  7. Select installation or upgrade option if replacing existing ESXi build
  8. Validate successful text-based initialization of hypervisor components
  9. Reboot host which then boots directly into ESXi hypervisor
  10. Customize host settings – NICs, DNS, syslog, password
  11. Enable host for remote management via SSH, vSphere Client

The host then runs the streamlined ESXi hypervisor OS optimized for rapidly deploying and managing virtual machines.

vSphere architecture and how hosts connect into infrastructure

Individual ESXi hosts provide the foundation for transforming physical data centers into virtualized private cloud environments managed by VMware vSphere. vSphere utilizes centralized management software, shared networking and storage to efficiently scale hosts into a unified infrastructure supporting thousands of workloads.

Key components enabling flexible management of many hosts in vSphere environments include:

vCenter Server – Centralized management application for monitoring and administering multiple ESXi hosts and associated virtual infrastructure. Enables advanced orchestration of host resources.

vSphere Client – Interface for connecting to vCenter or individual hosts to configure settings and manage virtual machines. New HTML5 web client provides portable access.

vSphere Networking – Host networking configurations for virtual switching, traffic shaping and firewall policies. Shared storage networks also interconnect host data stores.

Shared Storage – Central storage area network appliances, network attached storage, vSAN hyperconverged host storage etc. Enable virtual machines to migrate across compatible hosts.

Grouping hosts into vSphere clusters under common resource pools is key to achieving balanced utilization, performance and high availability for large-scale private cloud environments via capabilities like vMotion and Distributed Resource Scheduler.

Configuring and managing key host resources

Once installed, an ESXi host provides a foundation of physical compute, memory, storage and networking resources used to launch and run virtual machines according to real-time demands. Properly configuring host resources is critical for infrastructure stability and performance.

Some key aspects to configure include:

Hypervisor boot settings – Configure boot device priority, TPM support, boot delay etc. via BIOS and boot menu.

Date and time – Correct timezone and NTP time sync accuracy impacts functions relying on precise scheduling.

DNS and host name resolution – Ensures host visibility and access by IP/DNS fully qualified domain name.

Network adapters – Enable physical NICs, ensure proper media type selection and validate port group connectivity.

Data stores – Create VMFS volumes on connected disks and datastore clusters to house virtual machine files.

Remote management – Enable ESXi Direct Console User Interface via web client and/or SSH remote login.

CPU and Memory – Set reservations, shares and limits for host resources available to virtual machines.

Security – Isolate management network, authorize ESXi users/groups and enable lockdown, firewall rules.

Logging – Forward ESXi syslogs to a remote server for consolidated monitoring and troubleshooting.

Fine tuning host configurations for balanced resource allocation improves consolidated workload efficiency and stability.

Key usage scenarios and benefits

ESXi hosts running VMware’s market-leading hypervisor introduce transformational abstraction of IT infrastructure – on premises or in the cloud – to enable next-gen application modernization, cloud migration and workplace delivery of apps and data.

Some key ESXi host usage scenarios include:

Server Consolidation – Converging many legacy physical servers onto a smaller cluster of more powerful ESXi hosts driving up utilization rates.

Private/Hybrid Cloud – Pooling large collections of consistently configured hosts centrally orchestrated via vSphere to function as an agile, scalable compute fabric supporting thousands of workloads.

Virtual Desktops – Hosting many thousands of encrypted VM desktop images served up securely to remote workers via broker connection managers.

DevTest Platform – Rapidly spinning up transient sandbox VMs provisioned in seconds for code builds, test execution and patch staging required by Agile and DevOps teams.

Business Continuity – Combination of clustered shared storage, live VM mobility and distributed resource scheduling via vSphere keeps mission critical apps online through outages and maintenance events.

App Migration – Facilitates legacy app modernization by first encapsulating apps in VMs to be ported into hybrid cloud environments maintained by the same vSphere toolset.

For 15+ years VMware ESXi has been the industry standard for data center server virtualization, enabling substantial OpEx and CapEx cost savings while maximizing infrastructure flexibility and scalability.

Key takeaways

Some key takeaways about VMware ESXi hosts include:

  • ESXi is a bare-metal hypervisor from VMware for transforming x86 server hardware into consolidated hosts of many virtual machines
  • Direct installation on servers forgoes separate host operating system to maximize efficiency
  • Strict hardware compatibility requirements ensure reliable performance level for production workloads
  • Managed singly or collectively in vSphere clusters under centralized control planes
  • Enable private/hybrid cloud abstractions via enterprise-grade management interface
  • Hardware resources allocated dynamically to VMs using real-time optimization algorithms
  • Supports live workload mobility, rapid provisioning and business continuity protections
  • Mature platform for cost-effectively modernizing applications and workplace delivery

Understanding ESXi’s technical underpinnings and integration into VMware virtualization stack is key for smoothly operating infrastructure at scale supporting critical business systems.

Conclusion

VMware ESXi delivers proven, production-grade server virtualization, enabling IT organizations to unlock the flexibility and efficiency needed to propel core modernization initiatives around multi-cloud, apps and workplace. Centrally managed clusters of x86 ESXi hosts form the foundation powering many enterprise private clouds and underpinning hybrid cloud strategies.

Administering ESXi requires adjusting assumptions formed in an era dominated by physical servers – hosts have distinct lifecycle management needs around reservation/scheduling of memory, CPU and I/O resources shared dynamically across mutable workloads. But the dividends of workload abstraction and mobility introduced by ESXi and supplementary VMware innovations have entrenched virtualization at the heart of forward-looking data center architectures.

Frequently Asked Questions

Q: Can you install ESXi on any server?
A: No. ESXi has stringent hardware compatibility requirements maintained in VMware’s Hardware Compatibility List (HCL). Only specific, validated x86 server makes, models and component firmware/driver revisions are certified.

Q: Is VMware vSphere required for running ESXi hosts?
A: No. ESXi can run independently on standalone hosts not under vCenter management to operate a basic server virtualization environment. But the extensive capabilities of the vSphere stack makes centralized monitoring and resource orchestration of hosts most impactful.

Q: Can I install other software on an ESXi host?
A: No. The streamlined ESXi hypervisor has no general purpose OS functionality. Additional VIB system modules can be added to enable specialized hardware, but you cannot install conventional business applications on hosts.

Q: What hypervisors compete with VMware ESXi?
A: Major competitors in enterprise space include Microsoft Hyper-V, Red Hat Virtualization (RHEV), Citrix XenServer. Linux KVM and open source hypervisors are popular alternatives.

Q: What resources does the VMkernel manage?
A: VMkernel is the management operating system coordinating host physical resources – CPU, memory, networking and storage – utilized by virtual machines via abstractions like vCPU, virtual memory and virtual disks.

Q: Can you convert a physical machine into an ESXi host?
A: Yes. Using VMware’s P2V utility you can migrate a physical server OS, apps and data into a virtual machine cleanly rehosted on ESXi host hardware fitted for higher utilization via consolidation.

Q: Does ESXi support multi-core processors?
A: Yes. Symmetric multiprocessing (SMP) with multi-core Intel & AMD CPUs is fully supported to meet demanding workload requirements. Additional virtualization assists like EPT/RVI optimize physical core access.

Q: Can you boot ESXi hosts from USB or SD card?
A: Yes. In addition to SAS/SATA HDDs and SSDs, validated USB flash drives and host bus adapter SD cards can reliably boot the ESXi hypervisor.

Q: Do you need vCenter to manage ESXi?
A: No, ESXi has a built-in direct console and there are limitations, but you can perform stand-alone host administration through SSH or Web UIs. vCenter enables centralized monitoring, automation and resource orchestration across many hosts.

Q: How is vMotion enabled on ESXi hosts?
A: Workload mobility requires hosts join a cluster for coordination by vCenter and access to shared storage over high-speed lossless networking. vMotion seamlessly live migrates VMs without disconnecting.

Q: What are the most common ESXi host hardware failures?
A: Across server hardware components, the most common failures include fan/cooling components, power supplies, memory DIMMs, RAID controller battery backups, network cards and processor faults.

Q: Can you run containers on an ESXi host?
A: Not directly. You can run the Docker container engine inside a supported Linux VM on ESXi. Or you can utilize vSphere Integrated Containers to provision container workloads via VM templates.

Q: Does ESXi support 3D graphics acceleration?
A: Yes. For VDI 3D workloads, ESXi offers vDGA direct GPU pass-through. vGPU sharing and hardware accelerated graphics support is enabled for Windows/Linux VMs.

Q: Can I live migrate a VM from an ESXi host to a Hyper-V host?
A: Unfortunately not – VMware an Microsoft hypervisors don’t support interoperable migration between their respective platforms. You’d need to failover or shutdown/re-launch.

Q: What troubleshooting tools are available on ESXi hosts?
A: Built-in tools include esxtop for monitoring utilization, resxtop for I/O stats, esxcfg & esxcli for system management/configuration, vm-support for generating log bundles.

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