Synology DS1821 Virtual Machine Manager s White Paper - Page 19

When CPU compatibility mode is activated, VMM will hide CPU features that are not common to most processors from the VM. In effect, it will simulate the performance of an Intel Core 2 Duo processor. This allows running applications to continue successfully with a different processor. However, enabling the function can sharply reduce CPU performance. Among the functions most reliant on special CPU features are AES-256 encryption and compression processes, which can be heavily impacted when compatibility mode is enabled. In other words, performance penalties do not only depend on CPU speed, but also on the specific features included. Test results in the Comparing Configurations section compare the impact of CPU Compatibility Mode on cryptography, as well as on operations that rely less on special CPU features. For CPU compatibility mode to work, processors need to be from the same manufacturer. The option needs to be enabled before booting the VM's operating system. Enabling CPU compatibility mode is not necessary if you plan to shut down a VM and reboot it on another node. For a complete list of CPUs used in our products, refer to this up-to-date list. c. Storage nodes On storage nodes, compatible SSD cache can be utilized to significantly enhance read/ write performance. Random writes, especially, can benefit from a memory buffer. Using all-SSD Synology NAS for storage nodes is highly recommended to speed up I/O-intensive applications. An IOPS performance comparison for an HDD-based storage node with and without SSDcache can be found under Comparing Configurations. Learn more about installing additional SSD cache on your Synology NAS in Support Center. Synology supports a large number of SATA and SAS flash drives. In a previous white paper, we discussed how to increase the performance of Synology NAS and IP SAN. Keeping virtual disks and VMs on the same host Synology NAS achieves the best storage performance. d. Cluster networks When you configure separate computing and storage nodes, a cluster network is created. If it has to share its physical network with other hosts and applications, that can increase data transfer latency. Cluster networks have several other essential functions that can also be hampered by saturated network connections. A virtualization cluster ideally consists of an uneven number of nodes, which can then make decisions and monitor cluster health collectively by majority, or "quorum." A fast heartbeat connection allows nodes to do this and to properly order events in time. Delays on the network that affect the heartbeat can slow down all processes. Cluster networks should therefore ideally be isolated physically (using separate infrastructure) or logically (using VLAN and vSwitches). Each host Synology NAS must be assigned a static IP address. 17 Configuration Guide