File Systems and Network Attached Storage (NAS)
Disk subsystems provide block-oriented storage. For end users and for higher applications the handling of blocks addressed via cylinders, tracks and sectors is very cumbersome. File systems therefore represent an intermediate layer in the operating system that provides users with the familiar directories or folders and files and stores these on the block-oriented storage media so that they are hidden to the end users. This chapter introduces the basics of files systems and shows the role that they play in connection with storage networks.
This chapter first of all describes the fundamental requirements that are imposed upon file systems (Section 4.1). Then network file systems, file servers and the Network Attached Storage (NAS) product category are introduced (Section 4.2). We will then show how shared disk file systems can achieve a significantly higher performance than classical network file systems (Section 4.3). The chapter concludes with a comparison with block-oriented storage networks (Fibre Channel SAN, FCoE SAN, iSCSI SAN) and Network Attached Storage (NAS) (Section 4.4).
4.1 LOCAL FILE SYSTEMS
File systems form an intermediate layer between block-oriented hard disks and applications, with a volume manager often being used between the file system and the hard disk (Figure 4.1). Together, these manage the blocks of the disk and make these available to users and applications via the familiar directories and files.