1.2.3. Distributed Systems
- Horizontal scalability requires many tasks to be performed simultaneously (in parallel). As such, these tasks must have interprocess communication to coordinate their work. Further, a platform with horizontal scalability should be able to share tasks across multiple systems.
- Storage via local disks is not sufficient in addressing the requirements of horizontal scalability. Some form of distributed or shared storage is needed, one with a layer of abstraction that allows a single storage volume's capacity to grow seamlessly with the addition of new storage hardware.
- The most important duty in distributed computing is the management layer. This management layer coordinates all software and hardware components, efficiently managing communication, storage, and the usage of shared resources.
The most common way of communicating between computers is over Ethernet. Today, Gigabit Ethernet (GbE) is provided by default on systems, and most servers include 2-4 ports of Gigabit Ethernet. GbE provides good bandwidth and latency. This is the foundation of most distributed systems in use today. Even when systems include faster network hardware, it is still common to use GbE for a dedicated management interface.
Ten Gigabit Ethernet (10GbE) is rapidly growing in acceptance for high end and even mid-range servers. 10GbE provides ten times the bandwidth of GbE. One of its major advantages is with modern multi-core processors, where it restores the balance between communication and computing. You can compare a single core system using GbE to an eight core system using 10GbE. Used in this way, 10GbE is especially valuable for maintaining overall system performance and avoiding communication bottlenecks.
Infiniband offers even higher performance than 10GbE. In addition to TCP/IP and UDP network connections used with Ethernet, Infiniband also supports shared memory communication. This allows Infiniband to work between systems via remote direct memory access (RDMA).
RDMA over Converged Ethernet (RoCE) implements Infiniband-style communications (including RDMA) over a 10GbE infrastructure. Given the cost improvements associated with the growing volume of 10GbE products, it is reasonable to expect wider usage of RDMA and RoCE in a wide range of systems and applications.