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- Availability in this context denotes:
- Spacial - data or service is concurrently available to recipients/consumers in different locations rather than just one (many Virtual Machines using the same database that resides in distributed storage)
- Temporal continuity - data or service is kept available even in case of soft- or hardware failures ("High Availability")
Both of these aspects may seem very desirable, especially in cloud computing, but the downside is delivery speed in various forms. For example, distributed storage without high-end hardware may not have sufficient latency for storage-sensitive applications. Also, to keep the application availability rate high, there are software and several levels of hardware redundancy involved which means buying additional devices and keep them constantly running. - Locality denotes the physical distance of some functional domain from compute resource (local storage vs distributed storage)
While High Availability metrics are received by involving distributed and redundant resources, locality is also not free from redundancy cost, however it is usually the one of sub-server level, so definitely less expensive. Local storage has also much lower latency, but total capacity is very limited and, as data on this storage is not available to outer devices without additional control and services, it introduces additional data duplication need in addition to one that is meant for "High Availability".
Software- vs Hardware defined control of domains
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The bigger the amounts of data-flow between hardware devices, the bigger of a problem it tends to be. This traffic (and also In-DC traffic between silos, if larger DC is under consideration), is the one that measures the service system (Warren) efficiency. It's a two-fold problem, first the traffic that is generated by the clients, secondly the one that is generated by Warren as a management system. The goal of Warren is to reallocate resources to minimize in-DC traffic and in rare cases, it can, by doing so, destabilize the network flow for a short period of time. Management flow must always take precedence when client flow is causing problems, even if it decreases client throughput further. Because it’s purpose is to restore the previous state, or at least maximize the efficiency with the currently limited amount of available resources.
Existing SDN solution
Resources In general, all SDN systems are based on the same principles an in major part, derived from two prevalent frameworks for SDN generation. There are several types of protocols when it comes to network device configuration, among which, OpenFlow is still the most dominant one. Almost all needed routing protocols are also supported by all major SDN solutions.
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