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Unified CM virtualization and sizing

Verified 2026-09-25 · 52 sources · tier 2–5

Cisco Unified Communications Manager (Unified CM) runs as a virtualized application on supported hypervisors under strict host resource reservation and sizing rules 7​26​48. Sizing determines virtual machine specifications, node counts, and cluster capacities using defined configurations and tools 47​14​12.

Hypervisor Support and Deployment Models

Cisco Collaboration applications do not support any third-party public cloud IaaS offer, including VMware Cloud Foundation-based public cloud offers and on-premises hybrid-cloud extensions of public clouds 32. On 2025-10-07, Cisco announced its intent to support Nutanix AHV for the Unified CM portfolio, expecting general availability in early 2026, and noted that Unified CM historically supported only VMware ESXi 4.

For VMware vSphere ESXi environments, supported versions depend on the Unified CM release:

  • Unified CM 12.5(1) SU2 and later lists VMware vSphere ESXi 6.5, 6.7, and 7.0 U1 42.
  • Unified CM Version 14 lists VMware vSphere ESXi 6.7, 7.0 U1, and 8.0 U1 44.
  • Unified CM Version 15 lists VMware vSphere ESXi 7.0 U3 and 8.0 U1 48.
  • Unified CM Release 15SU4 notes that VMware vSphere ESXi 8.0 continues to be supported, while ESXi 7.0 and earlier have reached end of support from VMware by Broadcom 1.

Unified CM Release 15SU4 introduces support for two additional hypervisors:

  • Cisco NFVIS-for-UC: Release 15SU4 requires a minimum of NFVIS-for-UC 4.18.2a, with a minimum application release of 15SU4 (or X15.4 for Expressway) 2. NFVIS-for-UC supports only select Cisco appliances: Business Edition 6000 and 7000 (M5, M6, M7) and Expressway CE1400V (M7) 30. Cisco positions NFVIS-for-UC as a lightweight hypervisor built for collaboration workloads, calling it ideal for organizations with 200 to 5,000 users but usable at any size 31. The Register reported that NFVIS-for-UC hosts only Cisco calling applications, not general-purpose workloads, and framed it as a response to Broadcom's VMware licensing changes 29.
  • Nutanix AHV: Release 15SU4 supports Unified CM on Cisco Compute Hyperconverged with Nutanix (Cisco HCI nodes and connected compute nodes on HCI, HCIX, and UCS hardware), requiring a minimum of Nutanix AHV 10.0 and AOS 7.0 3.

On both NFVIS-for-UC and Nutanix AHV, 15SU4 supports Unified CM, Unified CM Session Management Edition, IM and Presence, Unity Connection, Emergency Responder, Expressway, and the Dedicated Instance Enhanced Survivability Node 28.

On Cisco Business Edition 6000/7000 appliances of generation M6 or later, the VMware vSphere ESXi licence must be a general-purpose licence 5.

Host Hardware and Sizing Rules

Physical host resources must satisfy strict allocation constraints:

  • CPU oversubscription: Physical CPU cores must not be oversubscribed for Cisco Collaboration VMs unless an application says otherwise; the host must possess at least as many physical cores as the total vCPUs of all its VMs 7. Hyperthreading should be enabled in the BIOS, but sizing VMs so that the total vCPU equals the number of ESXi logical processors is not supported unless an application specifically permits it 24.
  • CPU base frequencies: Sizing may not count Max Turbo Frequency, and CPU power-saving features that throttle the CPU are not supported for Collaboration VMs 33. Cisco defines small systems as under 1,000 users and under 2,500 devices (similar to Business Edition 6000 limits); for these, processors with a base frequency of 2.00 to 2.49 GHz are always supported 38.
  • Memory: Host physical memory must not be oversubscribed, meaning usable RAM must be at least the total vRAM of all VMs plus the memory needed by ESXi itself 26. ESXi 8.0 host memory is budgeted at a minimum of 8 GB, with 12 GB budgeted for typical production deployments 22.
  • Storage: Unless an application states otherwise, storage requires an average VM operating system latency per command within 25 ms 39.
  • Co-residency: Unless an application says otherwise, Collaboration applications may share a host with other Cisco Collaboration apps, other Cisco apps, and third-party apps, provided every application's VM placement and minimum hardware rules are met 6. UCCE and Cisco WebEx Meetings Server are named as having their own restrictions 6.

VM Sizing and Specifications

Unified CM VM configurations historically aligned directly to user tiers, whereas newer releases define recommended starting sizes:

  • Release 12.5(1) SU2 and later: VM configurations are named by user count (150, 1,000, 2,500, 7,500, and 10,000 users) 43. The 10,000-user configuration requires 4 vCPU at 2.50 GHz, 8 GB vRAM, and one 110 GB vDisk 43.
  • Versions 14 and 15: The virtualization page presents Small, Medium and Large as recommended starting points without user or device counts, and points to the Collaboration Sizing Tool (CST) for prescriptive VM specifications 47.

For Unified CM Version 14, a cluster node needs at least 2 vCPU, a 2.00 GHz physical CPU base frequency, 6 GB vRAM and one 80 GB vDisk 46. The Version 14 Large recommended starting point is 4 vCPU at 2.50+ GHz, 8 GB vRAM and one 110 GB vDisk, while the Medium starting point is 2 vCPU at 2.50+ GHz, 8 GB and 110 GB 45.

For Unified CM Version 15, a cluster node needs at least 2 vCPU, a physical CPU base frequency of at least 2.00 GHz, 10 GB vRAM, one 110 GB vDisk and 1 vNIC 51. Recommended starting points include:

  • The Version 15 Small recommended starting point is 2 vCPU at 2.00+ GHz, 10 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC 52.
  • The Version 15 Medium recommended starting point is 2 vCPU at 2.50+ GHz, 12 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC 50.
  • The Version 15 Large recommended starting point is 4 vCPU at 2.50+ GHz, 14 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC 49.

ESXi CPU reservations are hardcoded in the Cisco-provided OVA and must not be changed unless the application says so 8.

Cluster Boundaries and Capacities

Under Collaboration System Release 14 (CSR 14) sizing, cluster limits and architecture standards are defined as follows:

  • CSR 14 sizing describes three recommended Unified CM VM configurations (OVAs): Small, Medium and Large 18.
  • A standard Unified CM cluster may have at most 4 call-processing subscribers plus 4 standby, for 8 call-processing subscriber nodes in total 14.
  • A Unified CM cluster may have at most 21 server nodes in total, counting the publisher, TFTP and media servers 12.
  • Each Unified CM cluster supports configuration and registration of at most 50,000 secured or unsecured SCCP or SIP phones, and at most 50,000 CTI connections 13​11.
  • Once a cluster has more than 1,250 endpoints, it needs two TFTP server nodes and a dedicated publisher 17.
  • In CSR 14 sizing, the Large Unified CM OVA supports at most 12,500 users per node, assuming 1 device per user; with 2 devices per user, that falls to 6,250 users (12,500 devices) 10.
  • A megacluster is a Unified CM cluster with more than 4 pairs of call-processing subscribers, supporting up to 8 pairs within 21 server nodes, and customers must engage their Cisco account team, Cisco Advanced Services or a certified partner to deploy one 16.

The Collaboration 14 Preferred Architecture applies specific design baselines using the Medium Unified CM OVA:

  • It sizes up to 5,000 users/devices at 5 nodes (publisher, 2 TFTP, 1 subscriber pair) 35.
  • It sizes 5,000 to 10,000 users/devices at 7 nodes (publisher, 2 TFTP, 2 subscriber pairs) 35.
  • IM and Presence is sized as 1 node pair: the 5k-user OVA for fewer than 5,000 users or logged-in Jabber endpoints, and the 15k-user OVA for 5,000 to 15,000 34.

Maintenance and Reconfiguration Procedures

Downloading a new OVA is optional when upgrading Unified CM 15: if the system already runs on a VM and its deployment size has not changed, no new OVA is needed, while a new OVA is needed when the system size changes 27.

To change a Unified CM VM's vCPU, vRAM or vDisk, the Release 15 upgrade guide says to take a Cisco Disaster Recovery System (DRS) backup, shut down the VM, then edit the settings in the vSphere Client, updating the reservation value to match the new release's specifications 36. Expanding a Unified CM vDisk adds the space to the common partition on the next restart, but it does not increase the system's user capacity 19.

The Release 15 guide's ESXi upgrade procedure has 4 steps: move the Unified CM VM off the host (vMotion, or power down and copy), upgrade ESXi per VMware's procedure, verify the upgrade, then return the VM to the host 20.

See also

Applicability

Applies to: Cisco Collaboration applications (incl. Unified CM), Cisco Unified Communications Manager, Cisco NFVIS-for-UC, Cisco Business Edition 6000, and Cisco Unified CM IM. Deployments: on-premises. Sources checked 2026-09-25. The evidence covers releases 12.5(1) SU2 and later, 14, 15, and 15SU4 42​46​51​2.

What remains uncertain

  • Co-residency rules on NFVIS-for-UC vs Nutanix AHV vs ESXi are not covered by the sources below.
  • The procedure to move an existing Unified CM VM from ESXi to NFVIS-for-UC or AHV is not covered by the sources below.
  • Whether Unified CM supports VMware ESXi 9.x is not covered by the sources below.
  • Verifying Release 15 cluster maxima and per-OVA endpoint tables is not covered by the sources below.
  • Mapping Version 15 Small, Medium, and Large to user and device counts is not covered by the sources below.
  • Whether AHV and NFVIS VM specs and reservations match the ESXi OVA specs is not covered by the sources below.
  • The NFVIS-for-UC licensing model and pricing are not covered by the sources below.
  • The Unified CM policy on vMotion, HA, DRS, and snapshots is not covered by the sources below.

See also

Related to

  • Cisco Expressway clustering — The 15SU4 release notes list Expressway X15.4 alongside Unified CM as supported on NFVIS-for-UC and Nutanix AHV.
  • Planning a Unified CM upgrade — Changing VM size or hypervisor (ESXi to NFVIS-for-UC or Nutanix AHV) is typically done alongside a release upgrade; 15SU4 is the minimum release for the non-ESXi hypervisors.

Referenced by

  • Cisco Expressway clustering — Expressway VM sizes (Small/Medium/Large) and co-residency rules constrain which peers may be clustered and what capacity a cluster yields; proposed by this packet; not previously recorded.
  • Unified CM CTI and JTAPI integrations — CTI resources per subscriber VM and per cluster are a sizing input

Sources

  1. 1
    The 15SU4 release notes say VMware vSphere ESXi 8.0 continues to be supported, and that ESXi 7.0 and earlier have reached end of support from VMware by Broadcom.
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · New Hypervisor Support for On-premises Calling Solutions, VMware vSphere ESXi · Checked 2026-09-25
  2. 2
    Unified CM Release 15SU4 adds support for Cisco NFVIS-for-UC as a hypervisor, with a minimum of Release 15SU4 (X15.4 for Expressway) running on NFVIS-for-UC 4.18.2a.
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · New Hypervisor Support for On-premises Calling Solutions, Cisco NFVIS-for-UC · Checked 2026-09-25
  3. 3
    Release 15SU4 supports Unified CM on Cisco Compute Hyperconverged with Nutanix (Cisco HCI nodes and connected compute nodes on HCI, HCIX and UCS hardware), with a minimum of Nutanix AHV 10.0 and AOS 7.0.
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · New Hypervisor Support for On-premises Calling Solutions, Cisco Compute Hyperconverged with Nutanix (CCHN) · Checked 2026-09-25
  4. 4
    On 2025-10-07, Cisco announced its intent to support Nutanix AHV for the Unified CM portfolio and said it expected general availability to begin in early 2026. The same post said Unified CM had historically supported only VMware ESXi.
    Expanding Flexibility: Cisco Unified Communications Manager (UCM) to Support the Nutanix AHV Hypervisor · body paragraphs (announcement and timing) · Checked 2026-09-25
  5. 5
    On Cisco Business Edition 6000/7000 appliances of generation M6 or later, the VMware vSphere ESXi licence must be a general-purpose licence.
    Cisco Collaboration Infrastructure Requirements · Licensing options for VMware vSphere ESXi · Checked 2026-09-25
  6. 6
    Unless an application says otherwise, Collaboration applications may share a host with other Cisco Collaboration apps, other Cisco apps and third-party apps, provided every application's VM placement and minimum hardware rules are met. UCCE and Cisco WebEx Meetings Server are named as having their own restrictions.
    Cisco Collaboration Infrastructure Requirements · Introduction, Solution Special Requirements · Checked 2026-09-25
  7. 7
    Physical CPU cores must not be oversubscribed for Cisco Collaboration VMs unless an application says otherwise: the host must have at least as many physical cores as the total vCPUs of all its VMs.
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, VM Placement · Checked 2026-09-25
  8. 8
    ESXi CPU reservations are hardcoded in the Cisco-provided OVA and must not be changed unless the application says so.
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, VM Placement · Checked 2026-09-25
  9. 9
    CSR 14 sizing caps node capacity at 2,500 on Business Edition 6000H and 1,200 on Business Edition 6000M.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Endpoints section · Checked 2026-09-25
  10. 10
    In CSR 14 sizing, the Large Unified CM OVA supports at most 12,500 users per node, assuming one device per user. With two devices per user, that falls to 6,250 users (12,500 devices).
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Endpoints section, text around Table 1-4 · Checked 2026-09-25
  11. 11
    Each Unified CM cluster supports at most 50,000 CTI connections.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  12. 12
    A Unified CM cluster may have at most 21 server nodes in total, counting the publisher, TFTP and media servers.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  13. 13
    In Collaboration System Release 14 sizing, each Unified CM cluster supports configuration and registration of at most 50,000 secured or unsecured SCCP or SIP phones.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  14. 14
    A standard Unified CM cluster may have at most 4 call-processing subscribers plus 4 standby, for 8 call-processing subscriber nodes in total.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  15. 15
    CSR 14 Table 1-4 (maximum endpoints per VM configuration) gives 10,000 endpoints for the Medium OVA and 3,750 for the Small OVA.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Endpoints section, Table 1-4 Maximum Number of Endpoints Supported Per VM Configuration · Checked 2026-09-25
  16. 16
    A megacluster is a Unified CM cluster with more than 4 pairs of call-processing subscribers. It may have up to 8 pairs, still within 21 server nodes, and customers must engage their Cisco account team, Cisco Advanced Services or a certified partner to deploy one.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Megacluster section · Checked 2026-09-25
  17. 17
    Once a cluster has more than 1,250 endpoints, it needs two TFTP server nodes and a dedicated publisher.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  18. 18
    CSR 14 sizing describes three recommended Unified CM VM configurations (OVAs): Small, Medium and Large.
    Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14 · Virtual Nodes and Cluster Maximums · Checked 2026-09-25
  19. 19
    Expanding a Unified CM vDisk adds the space to the common partition on the next restart, but it does not increase the system's user capacity.
    Upgrade and Migration Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs - Change the Virtualization Software · Change Virtual Machine Configuration Specifications · Checked 2026-09-25
  20. 20
    The Release 15 guide's ESXi upgrade procedure has four steps: move the Unified CM VM off the host (vMotion, or power down and copy), upgrade ESXi per VMware's procedure, verify the upgrade, then return the VM to the host.
    Upgrade and Migration Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs - Change the Virtualization Software · Upgrade vSphere ESXi · Checked 2026-09-25
  21. 21
    The Version 15 virtualization page still lists ESXi 7.0 U3, while the 15SU4 release notes say ESXi 7.0 is past VMware end of support. The page's ESXi list is therefore probably out of date for 15SU4 and later.inferred
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · VMware vSphere ESXi paragraph, compared with cisco-virt-cucm-page Version 15 section · Checked 2026-09-25
  22. 22
    Cisco's infrastructure page budgets ESXi 8.0 host memory at a minimum of 8 GB, with 12 GB for typical production deployments.
    Cisco Collaboration Infrastructure Requirements · RAM Requirements, VM Placement (ESXi memory list) · Checked 2026-09-25
  23. 23
    Supported compute includes Cisco Business Edition 6000/7000 appliances, Cisco UCS B-, C- and X-Series, Cisco HyperFlex, and third-party blade or rack servers or hyperconverged infrastructure that meet Cisco's specifications.
    Cisco Collaboration Infrastructure Requirements · Hardware/Software Compatibility Requirements · Checked 2026-09-25
  24. 24
    Hyperthreading should be enabled in the BIOS, but sizing VMs so that the total vCPU equals the number of ESXi logical processors is not supported unless an application specifically allows it.
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, VM Placement (hyperthreading paragraph) · Checked 2026-09-25
  25. 25
    Cisco's Collaboration Infrastructure Requirements page states that VMware vSphere ESXi is the only supported hypervisor for Cisco Collaboration applications, naming Microsoft Hyper-V, Citrix Xen, Red Hat Virtualization and VMware Cloud Foundation as unsupported.disputed
    Cisco Collaboration Infrastructure Requirements · Supported Infrastructure section · Checked 2026-09-25
  26. 26
    Host physical memory must not be oversubscribed: usable RAM must be at least the total vRAM of all VMs plus the memory ESXi itself needs.
    Cisco Collaboration Infrastructure Requirements · RAM Requirements, VM Placement · Checked 2026-09-25
  27. 27
    Downloading a new OVA is optional when upgrading Unified CM 15: if the system already runs on a VM and its deployment size has not changed, no new OVA is needed. A new OVA is needed when the system size changes.
    Upgrade and Migration Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs - Change the Virtualization Software · Change the Virtualization Software chapter, OVA download task · Checked 2026-09-25
  28. 28
    On NFVIS-for-UC and Nutanix AHV, 15SU4 supports Unified CM, Unified CM Session Management Edition, IM and Presence, Unity Connection, Emergency Responder, Expressway and the Dedicated Instance Enhanced Survivability Node.
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · New Hypervisor Support for On-premises Calling Solutions, supported applications lists · Checked 2026-09-25
  29. 29
    The Register reported that NFVIS-for-UC hosts only Cisco calling applications, not general-purpose workloads, and framed it as a response to Broadcom's VMware licensing changes.
    Cisco set to release hypervisor as VMware alternative · article body · Checked 2026-09-25
  30. 30
    NFVIS-for-UC supports only select Cisco appliances: Business Edition 6000 and 7000 (M5, M6, M7) and Expressway CE1400V (M7).
    Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4 · New Hypervisor Support for On-premises Calling Solutions, Cisco NFVIS-for-UC, supported hardware · Checked 2026-09-25
  31. 31
    Cisco positions NFVIS-for-UC as a lightweight hypervisor built for collaboration workloads. It calls it ideal for organizations with 200 to 5,000 users but usable at any size.
    Expanding Flexibility for Cisco UCM with NFVIS-for-UC · body paragraphs (positioning) · Checked 2026-09-25
  32. 32
    Cisco Collaboration applications do not support any third-party public cloud IaaS offer, including VMware Cloud Foundation-based public cloud offers and on-premises hybrid-cloud extensions of public clouds.
    Cisco Collaboration Infrastructure Requirements · Supported Infrastructure section · Checked 2026-09-25
  33. 33
    Cisco sizing may not count Max Turbo Frequency, and CPU power-saving features that throttle the CPU are not supported for Collaboration VMs.
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, Processor Base Frequency · Checked 2026-09-25
  34. 34
    The Collaboration 14 Preferred Architecture sizes IM and Presence as one node pair: the 5k-user OVA for fewer than 5,000 users or logged-in Jabber endpoints, and the 15k-user OVA for 5,000 to 15,000.
    Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Sizing · Sizing, IM and Presence section · Checked 2026-09-25
  35. 35
    Cisco's Collaboration 14 Preferred Architecture uses the Medium Unified CM OVA. It sizes up to 5,000 users/devices at 5 nodes (publisher, 2 TFTP, 1 subscriber pair) and 5,000 to 10,000 at 7 nodes (publisher, 2 TFTP, 2 subscriber pairs).
    Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Sizing · Sizing, Unified CM section · Checked 2026-09-25
  36. 36
    To change a Unified CM VM's vCPU, vRAM or vDisk, the Release 15 upgrade guide says to take a DRS backup, shut down the VM, then edit the settings in the vSphere Client, updating the reservation value to match the new release's specifications.
    Upgrade and Migration Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs - Change the Virtualization Software · Change Virtual Machine Configuration Specifications · Checked 2026-09-25
  37. 37
    Because Version 14/15 Small is the only size allowing a 2.00 GHz base frequency, and Cisco only guarantees 2.00 to 2.49 GHz CPUs for small systems (under 1,000 users and 2,500 devices), Small most likely corresponds to that small-system envelope.inferred
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 recommended starting points table, read with cisco-virt-collab-infrastructure Processor Base Frequency · Checked 2026-09-25
  38. 38
    Cisco defines small systems as under 1,000 users and under 2,500 devices (similar to Business Edition 6000 limits). For these, processors with a base frequency of 2.00 to 2.49 GHz are always supported.
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, Processor Base Frequency · Checked 2026-09-25
  39. 39
    Unless an application says otherwise, Cisco Collaboration applications require storage with average VM operating system latency per command within 25 ms.
    Cisco Collaboration Infrastructure Requirements · Storage Requirements & Guidelines, VM Placement · Checked 2026-09-25
  40. 40
    Supported CPU families listed include Intel Xeon (Skylake through Granite Rapids) and AMD EPYC (3rd-gen Milan, 4th-gen Genoa and 5th-gen Turin).
    Cisco Collaboration Infrastructure Requirements · CPU Requirements, supported CPU architectures · Checked 2026-09-25
  41. 41
    Thin provisioning is allowed, but Cisco warns that running out of disk space on thin-provisioned storage will cause application instability and data corruption.
    Cisco Collaboration Infrastructure Requirements · Storage Requirements & Guidelines, provisioning · Checked 2026-09-25
  42. 42
    For Unified CM 12.5(1) SU2 and later, the virtualization page lists VMware vSphere ESXi 6.5, 6.7 and 7.0 U1.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 12.5(1) - SU2+ section · Checked 2026-09-25
  43. 43
    For 12.5(1) SU2 and later, Unified CM VM configurations are named by user count (150, 1,000, 2,500, 7,500 and 10,000 users). The 10,000-user configuration is 4 vCPU at 2.50 GHz, 8 GB vRAM and one 110 GB vDisk.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 12.5(1) - SU2+ section, user-based specifications table · Checked 2026-09-25
  44. 44
    Cisco's Unified CM virtualization page lists VMware vSphere ESXi 6.7, 7.0 U1 and 8.0 U1 as supported for Unified CM Version 14.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 14 section, Supported VMware vSphere ESXi · Checked 2026-09-25
  45. 45
    The Version 14 Large recommended starting point is 4 vCPU at 2.50+ GHz, 8 GB vRAM and one 110 GB vDisk. The Medium starting point is 2 vCPU at 2.50+ GHz, 8 GB and 110 GB.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 14 section, recommended starting points table, Medium and Large rows · Checked 2026-09-25
  46. 46
    For Unified CM Version 14, a cluster node needs at least 2 vCPU, a 2.00 GHz physical CPU base frequency, 6 GB vRAM and one 80 GB vDisk.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 14 section, UCM Cluster Node Minimums · Checked 2026-09-25
  47. 47
    For Versions 14 and 15, the Unified CM virtualization page presents Small, Medium and Large as recommended starting points without user or device counts, and points to the Collaboration Sizing Tool (CST) for prescriptive VM specifications.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 and Version 14 sections, text above the recommended starting points tables · Checked 2026-09-25
  48. 48
    Cisco's Unified CM virtualization page lists VMware vSphere ESXi 7.0 U3 and 8.0 U1 as supported for Unified CM Version 15.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 section, Supported VMware vSphere ESXi · Checked 2026-09-25
  49. 49
    The Version 15 Large recommended starting point is 4 vCPU at 2.50+ GHz, 14 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 section, recommended starting points table, Large row · Checked 2026-09-25
  50. 50
    The Version 15 Medium recommended starting point is 2 vCPU at 2.50+ GHz, 12 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 section, recommended starting points table, Medium row · Checked 2026-09-25
  51. 51
    For Unified CM Version 15, a cluster node needs at least 2 vCPU, a physical CPU base frequency of at least 2.00 GHz, 10 GB vRAM, one 110 GB vDisk and 1 vNIC.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 section, UCM Cluster Node Minimums · Checked 2026-09-25
  52. 52
    The Version 15 Small recommended starting point is 2 vCPU at 2.00+ GHz, 10 GB vRAM, one 110 GB vDisk and one 1GbE+ vNIC.
    Virtualization for Cisco Unified Communications Manager (CUCM) · Version 15 section, recommended starting points table, Small row · Checked 2026-09-25

Documents

tier 2 current vendor documentation

Cisco Collaboration Infrastructure Requirements

Cisco Systems · accessed 2026-09-25

tier 2 current vendor documentation

Cisco Collaboration Sizing Guide - Collaboration Sizing Guide for CSR 14

Cisco Systems · 2021-05-25 · accessed 2026-09-24

tier 2 current vendor documentation

Preferred Architecture for Cisco Collaboration 14 Enterprise On-Premises Deployments, CVD - Sizing

Cisco Systems · 2021-05-21 · accessed 2026-09-25

tier 2 current vendor documentation

Release Notes for Cisco Unified Communications Manager Release 15SU4a and the IM and Presence Service Release 15SU4

Cisco Systems, Inc. · 2026-03-17 · accessed 2026-09-04

tier 2 current vendor documentation

Upgrade and Migration Guide for Cisco Unified Communications Manager and the IM and Presence Service, Release 15 and SUs - Change the Virtualization Software

Cisco Systems · 2026-08-14 · accessed 2026-09-25

tier 2 current vendor documentation

Virtualization for Cisco Unified Communications Manager (CUCM)

Cisco Systems · accessed 2026-09-25

tier 4 archived vendor documentation

Expanding Flexibility for Cisco UCM with NFVIS-for-UC

Cisco Webex (blog.webex.com) · 2025-10-29 · accessed 2026-09-25

tier 4 archived vendor documentation

Expanding Flexibility: Cisco Unified Communications Manager (UCM) to Support the Nutanix AHV Hypervisor

Cisco Webex (blog.webex.com) · 2025-10-07 · accessed 2026-09-25

tier 5 independent technical research

Cisco set to release hypervisor as VMware alternative

The Register · 2026-02-16 · accessed 2026-09-25

Cite this page

APA

WarmTransfer. (2026, September 25). Unified CM virtualization and sizing. WarmTransfer. https://warmtransfer.net/knowledge/cucm-virtualization-sizing

BibTeX

@misc{warmtransfer-cucm-virtualization-sizing,
  title  = {Unified CM virtualization and sizing},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/cucm-virtualization-sizing},
  note   = {Verified 2026-09-25}
}