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Tru64 UNIX File Systems A-PDF Split DEMO Tru64 UNIX File Systems Overview The Tru64 UNIX operating system supports the following types of file systems: UNIX File System (UFS) -- a local file system ISO 9660 Compact Disk File System (CDFS) -- a standard CD-ROM file system Memory File System (MFS) -- a UFS that resides in memory for speed Network File System (NFS) -- a facility for sharing files in a heterogeneous network Advanced File System (AdvFS) -- a local, log-based file system discussed in Module 7 File on File Mounting File System (FFM) -- allows regular, character, or blockspecial files to be mounted over regular files for a STREAMS-based pipe Process File System (procfs) -- a local file system that enables running processes to be accessed and manipulated as files File Descriptor File System (fdfs) -- allows applications to reference a process's open file descriptors as if they were files DVD File System (dvdfs) -- provides the ability to mount and read UDF formatted Digital Versatile Disks on both single nodes and clusters AdvFS and UFS are the principal file systems used by applications and the components of the operating system. AdvFS is the default file system at installation time. Note UFS is read-only in TruCluster Server, and MFS is unsupported in TruCluster Server. Virtual File System The operating system supports multiple types of file systems by using a Virtual File System (VFS): VFS provides file-system independent support for system calls. Different file system types are not apparent to the general user. Figure A-1 illustrates the virtual file system interface providing access to other file systems. A­2 A-PDF Split DEMO Figure A-1 File System Interface VFS UFS AdvFS NFS CDFS sm0209 VFS sits logically on top of the other file systems. A file system call goes to a VFS routine that determines the file system type it applies to, then calls a specific file system routine. Accessing a File Through VFS The process to access a file through the virtual file system is as follows: 1. Each open file is represented by a vnode in the system vnode table. 2. A process accesses a file through a file descriptor in its file descriptor table. 3. This descriptor points to an entry in the system file table. 4. The system file table includes a pointer to the vnode table. 5. The vnode table points to the disk blocks. 6. A memory buffer cache holds currently used disk blocks, for faster access. Figure A-2 shows the process of accessing a file through VFS. Figure A-2 Accessing a File Through VFS Process Descriptor Table descriptor descriptor descriptor System Open File Table file structure file structure file structure file structure Vnode Table vnode vnode vnode Disk Buffer Cache sm0210 A­3 UFS File Systems A-PDF Split DEMO UFS File Systems UNIX File System UFS uses a large block size to maximize the amount of data transferred with each I/O request. UFS is also known as the Berkeley fast file system, developed by the University of Californ