Specification-Based Hardware Support

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Specs-Based Hardware Requirements for running Cisco Unified Communications on VMware ESXi 4.0 and later


Cisco supports running UC applications on VMware ESXi. Customers may choose one of two different support models for compute, network and storage hardware.

  • Tested Reference Configurations (TRC):
Select hardware configurations tested and documented for specific guaranteed performance, capacity and application co-residency scenarios running "full-load" UC VMs. Intended for customers who want a packaged solution from Cisco that is pre-engineered for a specific deployment scenario and/or customers who are not sufficiently experienced with hardware virtualization. See Tested Reference Configurations (TRC) for more information.
  • Specs-Based VMware Hardware Support:
A flexible support policy described in the remainder of this document. Intended for customers with extensive expertise in virtualization and server/storage sizing who wish to use their own hardware standards. This hardware has not been directly tested or documented by Cisco UC, but meets certain specifications for which UC applications are supported. Performance is not guaranteed, but the Tested Reference Configurations may be used for guidance when sizing hardware. Important: Customers who choose this option are responsible for sufficiently sizing hardware to meet UC VM performance needs at the level of load deployed. Customers are also responsible for resolving performance problems by adjusting either the hardware configuration or the VM deployment model. Cisco is not responsible for performance problems resulting from use of specs-based support when the problem can be resolved by migrating the virtual machine to a faster hardware platform, or by powering off or migrating some of the other virtual machines on the server. It is recommended to use the Tested Reference Configurations for guidelines on hardware sizing. It is not recommended to use slower speed processors than the Tested Reference Configurations unless the customer understands the deployments will have unknown and unspecified reduction in capacity/performance.
  • For example, the CUCM 7500 user OVA has been tested at full load on Tested Reference Configurations using dual Intel Xeon E5640 processor. It is not recommended to use a less powerful processor.

Customers who require maximum flexibility and are proficient with virtualization, including the above support implications, should use Specs-based VMware Hardware support. Customers who require a simplified solution with guaranteed performance, and who lack experience with virtualization, should use Tested Reference Configurations.

The following are identical regardless of the support model chosen:

  • Virtual machine (OVA) requirements
  • VMware product, version and feature support
  • VMware configuration requirements for UC
  • Application/VM Co-residency support (specifically regarding application mix, VM count per physical server, 3rd-party support, reservations, oversubscription)

The remainder of this document defines the requirements of the specs-based policy.

VMware vSphere and vCenter Requirements

Supported VMware products, versions and features under this specs-based policy are the same as with the TRCs (Tested Reference Configurations), and are detailed here.

VMware vCenter is a required component in any deployment using this specs-based policy.

Configuring vCenter to capture detailed logs, as shown in Figure 1 below, is strongly recommended. If not configured by default, Cisco TAC may request enabling these settings in order to troubleshoot problems. It is a requirement that the customer deployment of vCenter be able to capture Statistics Level 4 for all statistics levels for the maximum duration at each level.

Figure 1

VCenter SS.jpg

Processor Requirements

Servers must have Intel Xeon 5600 or 7500 series of processors. No other processor vendors or models are supported.

Total physical core count required is based on the sum of UC virtual machine core requirements and the co-residency support policy).

Minimum physical core speed required is based on what UC virtual machines will be used, and at what intended load per VM. Processors of Tested Reference Configurations are sized for full-load virtual machines. It is recommended to use processors with same or higher speeds, as Cisco UC does not test or document lower performance points.

Recall that physical CPU cores may not be over-subscribed for UC VMs at this time (one physical CPU core = one vCPU core).

Cisco TAC will not troubleshoot performance problems in deployments with insufficient physical cores.


The only supported server vendors are:

  • Cisco Unified Computing System
  • HP
  • IBM

Cisco UCS Express, Dell and all other server vendors are not supported at this time.

All servers used must be on the VMware Hardware Compatibility List for the version of ESXi you will be running, and must meet all other policy requirements such as required CPU.

Otherwise, any server model/generation from the above vendors that satisfies all other criteria of this policy is supported for UC.


Minimum physical RAM required is 2GB for ESXi plus the sum of UC virtual machines' vRAM.

Recall that physical memory may not be over-subscribed for UC VMs.

Aside from total physical RAM, UC does not mandate memory module size, density, speed or quantity - follow server vendor requirements for memory hardware configuration.

Cisco TAC will not troubleshoot performance problems in deployments with insufficient physical RAM.

IO Devices

All I/O controllers and adapters used must be on the VMware Hardware Compatibility List for the version of ESXi you will be running.

Only the following I/O Devices are supported:

  • HBA
    • FC – 2Gbps or faster
    • InfiniBand
  • NIC
    • Ethernet – 1Gbps or faster
    • NFS and iSCSI are supported, but require minimum 10Gbps and dedicated NIC for network storage access
  • Converged Network Adapter or Cisco VIC
    • FCoE + Ethernet – 10Gbps or faster
  • RAID Controllers for DAS
    • SAS
    • SAS SATA Combo
    • SAS-RAID
    • SATA

Note that diskless servers for "boot from SAN" (FC, iSCSI, or FCoE) are only supported for UC if the UC app supports both ESXi 4.1 and the "boot from SAN" feature on the VMware Requirements page.

The customer is responsible for configuring an adequate number of I/O devices to handle the aggregate load that the virtual machines running on the server will generate.

The customer is also responsible for configuring redundant interfaces on the server to handle component failures (e.g. redundant NIC, CNA, HBA or VIC adapters.)

There are no UC restrictions on hardware vendors for I/O Devices other than that VMware and the server vendor/model must both support them.

Cisco TAC will not troubleshoot performance problems in a deployment designed with insufficient I/O devices or overloaded I/O devices. For example, a single 100Mbps NIC servicing eight "CUCM 7500 user OVAs" would be both insufficent and overloaded.


Each OVA provided by Cisco for running a UC application has a published IOPS and disk space requirement. It is the responsibility of the customer to provide a storage system that exceeds the disk space (see Unified Communications Virtualization Downloads (including OVA/OVF Templates) and average IOPS requirements (see IO Operations Per Second (IOPS)) of the UC virtual machines they will be running on that storage system.

If you are using NFS, iSCSI, or FCoE for storage connectivity, the networking configuration must provide Cisco Platinum Class QOS (Fiber Channel Equivalent): http://www.cisco.com/en/US/docs/solutions/Enterprise/Data_Center/Virtualization/securecldg.html.

See also Shared Storage Considerations here.

It is not necessary to configure the storage to handle the simultaneous maximum IOPS load of every virtual machine on the storage system, but the customer must be aware of the excess capacity of the storage system and not, for example, run multiple software upgrades on the virtual machines such that the storage system is over extended.

The kernel disk command latency must not be greater than 2-3 ms and the physical device command latency must not be greater than 15-20 ms. When either of these metrics is not met, Cisco considers the storage system inadequate to serve the UC virtual machines. Cisco will not troubleshoot performance problems in an environment where either metric is not being met.

As a guideline, Cisco has found the use of 15K rpm SAS or FC drives in a RAID 5 configuration to work well. The number of drives used in the array is 5. The recommended size of the hard drives is 300 to 450GB. Recommended LUN size is 500GB to 1.5TB, so that not more than 10 virtual machines reside on a LUN - preferably 8 or less.

This is only a guideline, it is left to the customer to configure their storage for adequate performance and for the redundancy level desired.

Mechanical & Environmental Components

UC apps have no dependencies on form factor, rack mounting hardware, cable management hardware or power supplies. Redundant power supplies are strongly recommended for high availability.

Back to: Unified Communications in a Virtualized Environment

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