I/O refers to the process of requesting and writing data to a storage system. The process is done through I/O streams, where data is requested one block, file, or object at a time.
Parallel I/O refers to the process where multiple streams perform operations concurrently on the same storage system. This increases performance and reduces access times, as various files or blocks are read or written at the same time.
In comparison, serial I/O is the process of performing a single stream of I/O, which could lead to reduced performance and increased latency or access times.
Storage clusters, such as GlusterFS, take advantage of parallel I/O, since data is spread through multiple nodes, allowing for numerous clients to access data at the same time without any drop in latency or throughput.
