Technical FAQs

Hardware

What are the minimum system requirements for running Citrix Hypervisor?

For the minimum system requirements for this release, see System requirements.

Do I need a system with a 64-bit x86 processor to run Citrix Hypervisor?

Yes. Either an Intel VT or AMD-V 64-bit x86-based system with one or more CPUs is required to run all supported guest operating systems.

For more information about host system requirements, see System requirements.

Do I need a system with hardware virtualization support?

To run Windows operating systems or HVM Linux guests, you need a 64-bit x86 processor-based system that supports either Intel VT or AMD-V hardware virtualization technology in the processor and BIOS.

For more information about HVM Linux guests, see Linux VMs.

What systems are certified to run Citrix Hypervisor?

For a complete list of Citrix Hypervisor certified systems, see the Hardware Compatibility List (HCL).

Does Citrix Hypervisor support AMD Rapid Virtualization Indexing and Intel Extended Page Tables?

Yes. Citrix Hypervisor supports AMD Rapid Virtualization Indexing and Intel Extended Page Tables. Rapid Virtualization Indexing provides an implementation of nested tables technology used to further enhance performance of the Xen hypervisor. Extended Page Tables provide an implementation of hardware assisted paging used to further enhance performance of the Xen hypervisor.

Can Citrix Hypervisor run on a notebook or desktop-class systems?

Citrix Hypervisor runs on many notebook or desktop-class systems that conform to the minimum CPU requirements. However, Citrix only supports systems that have been certified and listed on the Hardware Compatibility List (HCL). Customers can choose to run on unsupported systems for demonstration and testing purposes; however, some features, such as power management capabilities, do not work.

Product Limits

Note:

For a complete list of Citrix Hypervisor supported limits, see Configuration Limits.

What is the maximum size of memory that Citrix Hypervisor can use on a host system?

Citrix Hypervisor host systems can use up to 5 TB of physical memory.

How many processors can Citrix Hypervisor use?

Citrix Hypervisor supports up to 288 logical processors per host. The maximum number of logical processors supported differs by CPU.

For more information, see the Hardware Compatibility List (HCL).

How many virtual machines can run on Citrix Hypervisor concurrently?

The maximum number of virtual machines (VMs) supported to run on a Citrix Hypervisor host is 1000. For systems running more than 500 VMs, Citrix recommends allocating 8 GB of RAM to Dom0. For information about configuring Dom0 memory, see CTX134951 - How to Configure dom0 Memory in XenServer 6.2 and Later.

For any particular system, the number of VMs that can run concurrently and with acceptable performance depends on the available resources and the VM workload. Citrix Hypervisor automatically scales the amount of memory allocated to the Control Domain (Dom0) based on the physical memory available.

Note:

If there are more than 50 VMs per host and the host physical memory is less than 48 GB, it might be advisable to override this setting. For more information, see Memory usage.

How many physical network interfaces does Citrix Hypervisor support?

Citrix Hypervisor supports up to 16 physical NIC ports. These NICs can be bonded to create up to 8 logical network bonds. Each bond can include up to 4 NICs.

How many virtual processors (vCPUs) can Citrix Hypervisor allocate to a VM?

Citrix Hypervisor supports up to 32 vCPUs per VM. The number of vCPUs that can be supported varies by the guest operating system.

Note:

Consult your guest OS documentation to ensure that you do not exceed the supported limits

How much memory can Citrix Hypervisor allocate to a VM?

Citrix Hypervisor supports up to 1.5 TB per guest. The amount of memory that can be supported varies by the guest operating system.

Note:

The maximum amount of physical memory addressable by your operating system varies. Setting the memory to a level greater than the operating system supported limit can lead to performance issues within your guest. Some 32-bit Windows operating systems can support more than 4 GB of RAM through use of the physical address extension (PAE) mode. The limit for 32-bit PV Virtual Machines is 64 GB. For more information, see your guest operating system documentation and supported guest operating systems.

How many virtual disk images (VDIs) can Citrix Hypervisor allocate to a VM?

Citrix Hypervisor can allocate up to 255 VDIs including a virtual DVD-ROM device per VM.

Note:

The maximum number of VDIs supported depends on the guest operating system. Consult your guest OS documentation to ensure that you do not exceed the supported limits.

How many virtual network interfaces can Citrix Hypervisor allocate to a VM?

Citrix Hypervisor can allocate up to 7 virtual NICs per VM. The number of virtual NICs that can be supported varies by the guest operating system.

Resource Sharing

How are processing resources split between VMs?

Citrix Hypervisor splits processing resources between vCPUs using a fair-share balancing algorithm. This algorithm ensures that all VMs get their share of the processing resources of the system.

How does Citrix Hypervisor choose which physical processors it allocates to the VM?

Citrix Hypervisor doesn’t statically allocate physical processors to any specific VM. Instead, Citrix Hypervisor dynamically allocates, depending on load, any available logical processors to the VM. This dynamic allocation ensures that processor cycles are used efficiently because the VM can run wherever there is spare capacity.

How are disk I/O resources split between the VMs?

Citrix Hypervisor uses a fair-share resource split for disk I/O resources between VMs. You can also provide a VM higher or lower priority access to disk I/O resources.

How are network I/O resources split between the VMs?

Citrix Hypervisor uses a fair share resource split for network I/O resources between the VMs. You can also control bandwidth-throttling limits per VM by using the Open vSwitch.

Guest Operating Systems

Can Citrix Hypervisor run 32-bit operating systems as guests?

Yes. For more information, see Supported guest operating systems.

Can Citrix Hypervisor run 64-bit operating systems as guests?

Yes. For more information, see Supported guest operating systems.

Which versions of Microsoft Windows can run as guests on Citrix Hypervisor?

For a list of supported Windows guest operating systems, see Supported guest operating systems.

Which versions of Linux can run as guests on Citrix Hypervisor?

For a list of supported Linux guest operating systems, see Supported guest operating systems.

Can I run different versions of the supported operating systems or other unlisted operating systems?

Citrix only supports operating systems (OS) under OS vendor support. Although unsupported operating systems might continue to function, we might ask you to upgrade to a supported OS service pack before we can investigate any issues.

Applicable drivers might not be available for OS versions that are unsupported. Without the drivers, these OS versions do not function with optimized performance.

It’s often possible to install other distributions of Linux. However, Citrix can only support the operating systems listed in Supported guest operating systems. We might ask you to switch to a supported OS before issues we can investigate any issues.

Does Citrix Hypervisor support FreeBSD, NetBSD, or any other BSD variants as a guest operating system?

Citrix Hypervisor doesn’t support any BSD-based guest operating systems for general-purpose virtualization deployments. However, FreeBSD VMs running on Citrix Hypervisor have been certified for use in specific Citrix products.

What are the Citrix VM Tools?

The Citrix VM Tools are software packages for Windows and Linux-based guest operating systems. For Windows operation systems, the Citrix VM Tools include high-performance I/O drivers (PV drivers) and the Management Agent. For Linux-based operating systems, the Citrix VM Tools include a Guest Agent that provides additional information about the VM to the Citrix Hypervisor host. For more information, see Citrix VM Tools.

XenCenter

Do I have to run XenCenter on a Windows computer?

Yes. The XenCenter management console runs on a Windows operating system. For information about the system requirements, see System requirements

If you don’t want to run Windows, you can manage your Citrix Hypervisor hosts and pools by using the xe CLI or by using xsconsole, a system configuration console.

Can I log on to XenCenter using my Active Directory user accounts?

Yes. You can set up XenCenter login requests to use Active Directory on all editions of Citrix Hypervisor.

Can I restrict access of certain functions within XenCenter, to certain users?

Yes. The Role Based Access Control feature combined with Active Directory authentication can restrict access for users in XenCenter.

Can I use a single XenCenter console to connect to multiple Citrix Hypervisor hosts?

Yes. You can use a single XenCenter console to connect to multiple Citrix Hypervisor host systems.

Can I use XenCenter to connect to multiple hosts running different versions of Citrix Hypervisor?

Yes. XenCenter is backward compatible with multiple host systems running different versions of Citrix Hypervisor that are currently supported.

Can I use XenCenter to connect to multiple resource pools?

Yes. You can connect to multiple resource pools from a single XenCenter console.

How can I gain access to the console of Linux-based VM?

The Console tab in XenCenter provides access to the text-based and graphical consoles of VMs running Linux-based operating systems. Before you can connect with the graphical console of a Linux VM, ensure that the VNC server and an X display manager are installed on the VM and properly configured.

XenCenter also enables you to connect to Linux VMs over SSH by using the Open SSH Console option on the Console tab of the VM.

How can I gain access to the console of a Windows-based VM?

XenCenter provides access to the emulated graphics for a Windows VM. If XenCenter detects remote desktop capabilities on the VM, XenCenter provides a quick connect button to launch a built-in RDP client that connects to the VM. Or, you can connect directly to your guests by using external remote desktop software.

Command line interface (CLI)

Does Citrix Hypervisor include a CLI?

Yes. All editions of Citrix Hypervisor include a full command line interface (CLI) – known as xe.

Can I access the Citrix Hypervisor CLI directly on the host?

Yes. You can access the CLI by using a screen and keyboard connected directly to the host, or through a terminal emulator connected to the serial port of the host.

Can I access the Citrix Hypervisor CLI from a remote system?

Yes. Citrix ships the xe CLI, which can be installed on Windows and 64-bit Linux machines to control Citrix Hypervisor remotely. You can also use XenCenter to access the console of the host from the Console tab.

Can I use the Citrix Hypervisor CLI using my Active Directory user accounts?

Yes. You can log in using Active Directory on all editions of Citrix Hypervisor.

Can I restrict access the use of certain CLI commands to certain users?

Yes. You can restrict user access on the Citrix Hypervisor CLI.

VMs

Can VMs created with VMware or Hyper-V run on Citrix Hypervisor?

Yes. You can export and import VMs using the industry-standard OVF format.

You can also convert VMs in batches using Citrix Hypervisor Conversion Manager. Third-party tools are also available. For more information, see Conversion Manager.

What types of installation media can I use to install a guest operating system?

You can install a guest operating system by using:

  • A CD in the CD-ROM drive of the host
  • A virtual CD-ROM drive using technology such as iLO or DRAC
  • Placing ISO images on to a shared network drive
  • Network install where supported by the specific guest.

For more information, see Manage Virtual Machines.

Can I make a clone of an existing VM?

Yes. Any VM created on Citrix Hypervisor can be cloned or converted into a VM template. A VM template can then be used to create more VMs.

Can VMs be exported from one version of Citrix Hypervisor and moved to another?

Yes. VMs exported from older versions of Citrix Hypervisor can be imported to a newer version.

Can I convert a VM from the open-source version of Xen to Citrix Hypervisor?

No.

Does Citrix Hypervisor provide disk snapshot capabilities for VMs?

Yes. Citrix Hypervisor supports snapshotting in all editions. For more information, see VM Snapshots.

Storage

What types of local storage can be used with Citrix Hypervisor?

Citrix Hypervisor supports local storage such as SATA and SAS.

What type of SAN/NAS storage can be used with Citrix Hypervisor?

Citrix Hypervisor supports Fibre Channel, FCoE, Hardware-based iSCSI (HBA), iSCSI, NFS, and SMB storage repositories. For more information, see Storage and the Hardware Compatibility List.

Does Citrix Hypervisor support software-based iSCSI?

Yes. Citrix Hypervisor includes a built-in software-based iSCSI initiator (open-iSCSI).

What version of NFS is required for remote storage use?

Citrix Hypervisor requires NFSv3 or NFSv4 over TCP for remote storage use. Citrix Hypervisor currently does not support NFS over User Datagram Protocol (UDP).

Can I use software-based NFS running on a general-purpose server for remote shared storage?

Yes. Although Citrix recommends using a dedicated NAS device with NFSv3 or NFSv4 with high-speed non-volatile caching to achieve acceptable levels of I/O performance.

Can I boot a Citrix Hypervisor host system from an iSCSI, Fibre Channel or FCoE SAN?

Yes. Citrix Hypervisor supports Boot from SAN using Fibre Channel, FCoE, or iSCSI HBAs.

Can I boot a Citrix Hypervisor host using UEFI?

Yes. Citrix Hypervisor supports booting from BIOS and UEFI.

Does Citrix Hypervisor support Multipath I/O (MPIO) for storage connections?

Yes. Citrix recommends using multipath for resilient storage connections.

Does Citrix Hypervisor support a software-based RAID implementation?

No. Citrix Hypervisor doesn’t support software RAID.

Does Citrix Hypervisor support HostRAID or FakeRAID solutions?

No. Citrix Hypervisor doesn’t support proprietary RAID-like solutions, such as HostRAID or FakeRAID.

Does Citrix Hypervisor support thin cloning of existing VMs?

Yes. Thin cloning is available on local disks formatted as EXT3, in addition to NFS and SMB storage repositories.

Does Citrix Hypervisor support Distributed Replicated Block Device (DRBD) storage?

No. Citrix Hypervisor doesn’t support DRBD.

Does Citrix Hypervisor support ATA over Ethernet?

No. Citrix Hypervisor doesn’t support ATA over Ethernet-based storage.

Networking

Can I create private networks that isolate groups of VMs?

Yes. You can create a private network on a single host for resident VMs. With the vSwitch Controller appliance, you also can create private networks that span multiple hosts with or without encryption.

Does Citrix Hypervisor support multiple physical network connections?

Yes. You can connect to or associate multiple physical networks that attach to different network interfaces on the physical host system.

Can VMs connect to multiple networks?

Yes. VMs can connect to any network available to the host.

Does Citrix Hypervisor support IPv6?

Guest VMs hosted on Citrix Hypervisor can use any combination of IPv4 and IPv6 configured addresses.

However, Citrix Hypervisor doesn’t support the use of IPv6 in its Control Domain (Dom0). You can’t use IPv6 for the host management network or the storage network. IPv4 must be available for the Citrix Hypervisor host to use.

Does Citrix Hypervisor support VLANs on a physical network interface?

Yes. Citrix Hypervisor supports assigning VM networks to specified VLANs.

Do Citrix Hypervisor virtual networks pass all network traffic to all VMs?

No. Citrix Hypervisor uses Open vSwitch (OVS), which acts as a Layer 2 switch. A VM only sees traffic for that VM. Additionally, the multitenancy support in Citrix Hypervisor enables increased levels of isolation and security.

Do the virtual network interfaces and networks support promiscuous mode?

Yes. Virtual network interfaces can be configured for promiscuous mode, which enables you to see all traffic on a virtual switch. For more information about promiscuous mode configuration, see the following Knowledge Center articles:

Additionally, the Open vSwitch enables configuration of RSPAN to capture network traffic.

Does Citrix Hypervisor support bonding or teaming of physical network interfaces?

Yes. Citrix Hypervisor supports physical network interface bonding for failover and link aggregation with optional LACP support. For more information, see Networking.

Memory

How much memory is consumed by running Citrix Hypervisor?

Three components contribute to the memory footprint of a Citrix Hypervisor host.

  1. The Xen hypervisor
  2. The Control Domain on the host (dom0)
  3. The Citrix Hypervisor Crash Kernel

The amount of memory required to run dom0 is adjusted automatically. The amount of memory allocated is based on the amount of physical memory on the host as shown in the following table:

Host Memory (GB) Control Domain Memory Allocated (MB)
<24 752
24–47 2048
48–63 3072
64–1024 4096

Note:

The amount of memory allocated to the Control Domain can be increased beyond the amounts shown in the preceding table. However, you must only increase this allocation under the guidance of Citrix Support.

In XenCenter, the Xen field in the Memory tab reports the memory used by the Control Domain, by the Xen hypervisor itself, and by the Citrix Hypervisor Crash Kernel. The amount of memory used by the hypervisor is larger for hosts with more memory.

For more information, see Memory usage

Does Citrix Hypervisor optimize VM memory usage?

Yes. Citrix Hypervisor uses Dynamic Memory Control (DMC) to adjust automatically the memory of running VMs. These adjustments keep the amount of memory allocated to each VM between specified minimum and maximum memory values, guaranteeing performance and permitting greater VM density.

For more information, see VM memory.

Resource Pools

What is a Resource Pool?

A resource pool is a collection of a set of Citrix Hypervisor hosts managed as a unit. Typically, a resource pool shares some amount of networked storage to allow VMs to be rapidly migrated from one host to another within the pool. For more information, see Hosts and resource pools.

Does Citrix Hypervisor require a dedicated host to manage a resource pool?

No. A single host in the pool must be specified as the Pool Master. The Pool Master controls all administrative activities required on the pool. This design means that there is no external single point of failure. If the Pool Master fails, other hosts in the pool continue to operate, and the resident VMs continue to run as normal. If the Pool Master cannot come back online, Citrix Hypervisor promotes one of the other hosts in the pool to master to regain control of the pool.

This process is automated with the High Availability feature. For more information, see High availability.

Where is the configuration data for a resource pool stored?

A copy of the configuration data is stored on every host in the resource pool. If the current pool master fails, this data enables any host in the resource pool to become the new pool master.

What types of configurations can be made at the Resource Pool level?

Shared remote storage and networking configurations can be made at the resource-pool level. When a configuration is shared on the Resource Pool, the master system automatically propagates configuration changes to all the member systems.

Are new host systems added to a Resource Pool automatically configured with shared settings?

Yes. Any new host systems added to a Resource Pool automatically receive the same configurations for shared storage and network settings.

Can I use different types of CPUs in the same Citrix Hypervisor resource pool?

Yes. Citrix recommends that the same CPU type is used throughout the pool (homogeneous resource pool). However, it is possible for hosts with different CPU types to join a pool (heterogeneous), provided the CPUs are from the same vendor.

For more information, see Hosts and resource pools.

For updated information about the support for feature masking for specific CPU types, see Hardware Compatibility List.

Live Migration (formerly XenMotion)

Can I move a running VM from one host to another?

With live migration you can move running VMs when hosts share the same storage (in a pool).

Additionally, storage live migration allows migration between hosts that do not share storage. VMs can be migrated within or across pools.

High Availability

Does Citrix Hypervisor offer High Availability features?

Yes. If High Availability (HA) is enabled, Citrix Hypervisor continually monitors the health of the hosts in a pool. If HA detects that a host is impaired, the host is automatically shut down. This action allows for VMs to be restarted safely on an alternative healthy host.

Does Citrix Hypervisor High Availability support local storage?

No. If you want to use HA, shared storage is required. This shared storage enables VMs to be relocated if a host fails. However, HA allows VMs that are stored on local storage to be marked for automatic restart when the host recovers after a reboot.

Can I use HA to automatically sequence the restart of recovered VMs?

Yes. HA configuration allows you to define the order that VMs are started. This capability enables VMs that depend on one another to be sequenced automatically.

Performance Metrics

Do the Citrix Hypervisor management tools collect performance information?

Yes. Citrix Hypervisor provides detailed monitoring of performance metrics. These metrics include CPU, memory, disk, network, C-state/P-state information, and storage. Where appropriate, these metrics are available on a per-host and a per-VM basis. Performance metrics are available directly (exposed as Round Robin Databases), or can be accessed and viewed graphically in XenCenter or other third-party applications. For more information, see Monitor and manage your deployment.

How are Citrix Hypervisor performance metrics gathered?

Data for the Citrix Hypervisor performance metrics are collected from various sources. These sources include the Xen hypervisor, Dom0, standard Linux interfaces, and standard Windows interfaces such as WMI.

Does XenCenter display performance metrics in real time?

Yes. XenCenter displays real-time performance metrics on the Performance tab for each running VM as well as for the Citrix Hypervisor host. You can customize the metrics that are displayed.

Does XenCenter store and display historic performance metrics?

Yes. Citrix Hypervisor keeps performance metrics from the last year (with decreasing granularity). XenCenter provides a visualization of these metrics in real-time graphical displays.

Installation

Does Citrix Hypervisor install on top of systems that are already running an existing operating system?

No. Citrix Hypervisor installs directly on bare-metal hardware, avoiding the complexity, overhead, and performance bottlenecks of an underlying operating system.

Can I upgrade an existing Citrix Hypervisor or XenServer installation to a newer version?

Yes. If you have already installed a supported version of Citrix Hypervisor or XenServer you can update or upgrade to a newer version of Citrix Hypervisor instead of doing a fresh installation. For more information, see Update and Upgrade.

Can I upgrade from an out-of-support version of Citrix Hypervisor or XenServer installation to this version?

If your existing version of Citrix Hypervisor or XenServer is no longer in support, you cannot upgrade or update directly to the latest version of Citrix Hypervisor.

  • For XenServer and 6.5 Service Pack 1, you can first upgrade to XenServer 7.1 Cumulative Update 2 and then upgrade from XenServer 7.1 Cumulative Update 2 to Citrix Hypervisor 8.0.
  • For other 6.x versions of XenServer, you cannot upgrade to the latest version and must create a fresh installation of Citrix Hypervisor 8.0.
  • For out-of-support 7.x current releases of XenServer, you cannot upgrade to the latest version and must create a fresh installation of Citrix Hypervisor 8.0.

Any other upgrade path for these out-of-support versions is not supported.

How much local storage does Citrix Hypervisor require for installation on the physical host system?

Citrix Hypervisor requires a minimum of 46 GB of local storage on the physical host system.

Can I use PXE to do a network installation of Citrix Hypervisor on the host system?

Yes. You can install Citrix Hypervisor on the host system using PXE. You can also automatically install Citrix Hypervisor using PXE by creating a pre-configured answer file.

Does the Xen hypervisor run on Linux?

No. Xen is a Type 1 hypervisor that runs directly on the host hardware (“bare metal”). After the hypervisor loads, it starts the privileged management domain – the Control Domain, which contains a minimal Linux environment.

Where does Citrix Hypervisor get its device driver support?

Citrix Hypervisor uses the device drivers available from the Linux kernel. As a result, Citrix Hypervisor runs on a wide variety of hardware and storage devices. However, Citrix recommends that you use certified device drivers.

For more information, see the Hardware Compatibility List.

Licensing

How do I license Citrix Hypervisor?

For information about Citrix Hypervisor licensing, see Licensing

Technical Support

Does Citrix provide direct technical support for Citrix Hypervisor?

Yes. For more information, visit Citrix Support and Services.

Can I get technical support for Citrix Hypervisor and other Citrix products on a single support contract?

Yes. Citrix provides Technical Support contracts that allow you to open support incidents on Citrix Hypervisor, as well as other Citrix products.

For more information, visit Citrix Support and Services.

Do I have to buy a Citrix technical support contract at the same time as I buy Citrix Hypervisor?

No. You can buy a technical support contract from Citrix either at product point-of-sale or at another time.

Are there alternative channels for getting technical support for Citrix Hypervisor?

Yes. There are several alternative channels for getting technical support for Citrix Hypervisor. You can also use Citrix Support Knowledge Center, visit our forums, or contract with authorized Citrix Hypervisor partners who offer technical support services.

Does Citrix provide technical support for the open-source Xen project?

No. Citrix doesn’t provide technical support for the open-source Xen project. For more information, visit http://www.xen.org/.

Can I open a technical support incident with Citrix if I’m experiencing a non-technical issue?

No. Raise any non-technical issues with Citrix Hypervisor through Citrix Customer Service. For example, issues to do with software maintenance, licensing, administrative support, and order confirmation.