3
I/O Techniques
Computers generate, process and delete data. However, they can only store data for very short periods. Therefore, computers move data to storage devices such as tape libraries and the disk subsystems discussed in the previous chapter for long-term storage and fetch it back from these storage media for further processing. So-called I/O techniques realise the data transfer between computers and storage devices. This chapter describes I/O techniques that are currently in use or that the authors believe will most probably be used in the coming years.
This chapter first considers the I/O path from the CPU to the storage system (Section 3.1). An important technique for the realisation of the I/O path is Small Computer System Interface (SCSI, Section 3.2). To be precise, SCSI defines a medium (SCSI cable) and a communication protocol (SCSI protocol). The idea of Fibre Channel SAN is to replace the SCSI cable by a network that is realised using Fibre Channel technology: servers and storage devices exchange data as before using SCSI commands, but the data is transmitted via a Fibre Channel network and not via a SCSI cable (Sections 3.3, 3.4). An alternative to Fibre Channel SAN is IP storage. Like Fibre Channel, IP storage connects several servers and storage devices via a network on which data exchange takes place using the SCSI protocol. In contrast to Fibre Channel, however, the devices are connected by TCP/IP and Ethernet (Section 3.5). InfiniBand (Section 3.6) and Fibre ...
