Synology SA3400 Virtual Machine Manager s White Paper - Page 13

2. CPU and Memory Requirements The two parameters most likely to constrain your virtual ambitions are computing power and available memory. A VM's computing resources consist of virtual CPU cores (vCPU) and virtual RAM (vRAM), whose performance depends on their physical equivalents on the host. Assigning virtual CPUs Users can assign more vCPUs than there are physical cores to increase VM density and host utilization. Up to two or four (in VMM Pro) vCPUs can be created per physical CPU thread. However, CPU usage must be closely watched, as insufficient capacity can slow common processes down extremely or even precipitate crashes. Thread Windows Assigning Virtual Processors Synology NAS or PC Client C2 Datacenter Reserved CPU threadFisle File File 1 2 1 2 1 2 1 2 Filename Filename SSL Filename UvsDeSrM PC File DSM password SynologUy bpuasnstwuord Task password RHEL CPU vCPU Data V1 Data DSM Hyper Backup Account Explorer Data Figure 4: In this example, four CPU threads on two physical CPU cores are reserved for one Ubuntu Linux VM, while Synology VMM divides the other vCPUs over four remaining non-reserved threads based on relative load. Users can specify the number of vCPUs they wish to assign to each VM and whether these are to share physical CPU resources, or run on reserved CPU threads. Virtual Machine Manager automatically balances loads between non-reserved CPU threads. In VMM Pro, users can assign VMs relative weight, giving important services higher-priority access to the physical CPU. Dedicated physical CPU threads can be reserved for VMs running essential services, ensuring they can use the full capacity of one or more CPU threads. Higher-spec Synology NAS models, including the XS and FS series, sport higher-performance CPUs that can handle many applications. These are recommended for use as virtual host. In practice, RAM memory will often present the main bottleneck. Reserving system memory Unlike CPU capacity, RAM memory is reserved for each VM and for that VM only. That means depending on your VM specifications, RAM may provide a hard upper limit for the number of 11 Configuration Guide