CUCM upgrades (e.g., 12.5 → 14 → 15) often increase requirements. A VM that barely runs CUCM 12.5 may fail pre-upgrade checks for version 15.
To host these virtual machines, you generally choose between two paths: Cisco UCS Tested Reference Configurations (TRC)
Whether you’re deploying on Cisco’s UC on UCS hardware, third-party servers, or virtual machines, getting the specs wrong leads to choppy audio, failed failovers, and support headaches. cucm hardware requirements
Cisco no longer supports "bare-metal" installations on proprietary hardware for modern versions of CUCM (Version 10.x and later). Instead, CUCM runs as a virtual machine (VM) on Cisco Unified Computing System (UCS) servers or approved third-party "specs-based" hardware. Key Hypervisor Requirements VMware vSphere ESXi is the industry standard.
Cisco publishes OVA templates with specific vCPU, RAM, and disk allocations. These vary by (measured by subscribers and devices). CUCM upgrades (e
The critical metric for storage hardware is IOPS (Input/Output Operations Per Second). CUCM generates a constant stream of database transactions, logs, and CDR (Call Detail Records). If the underlying hardware uses slow mechanical hard drives (HDDs) rather than Solid State Drives (SSDs), the database performance degrades. Furthermore, specific versions of CUCM mandate a particular disk size (e.g., 80 GB or 110 GB). While this seems small by modern standards, it is a strict requirement; the installation wizard will often fail if the virtual disk does not meet the exact size specified in the OVA template.
Hardware requirements aren't just about a single server; they are about the cluster. A standard CUCM deployment requires at least two nodes: Holds the primary database. Subscriber: Handles active call processing. Cisco publishes OVA templates with specific vCPU, RAM,
✅ Server on Cisco HCL (UCS or approved third-party) ✅ VMware ESXi 6.7 or later (vCenter optional but helpful) ✅ OVA template matching your user/device count ✅ Memory reservation = allocated RAM ✅ Separate datastore for CUCM VMs (avoid contention) ✅ NTP configured at host level (CUCM is extremely NTP-sensitive) ✅ DNS & reverse DNS working for all nodes
Fiber Channel SAN, iSCSI SAN, or high-performance local RAID.