Overview of File Systems
A file system is a structure of directories that is used to organize and store files. The term file system is used to describe the following:
A particular type of file system: disk-based, network-based, or virtual
The entire file tree, begining with the root directory
The data structure of a disk slice or other media storage device
A portion of a file tree structure that is attached to a mount point on the main file tree so that the files are accessible
Usually, you can tell from the context which meaning is intended.
The Solaris operating environment uses the virtual file system (VFS) architecture, which provides a standard interface for different file system types. The VFS architecture enables the kernel to handle basic operations, such as reading, writing, and listing files, and makes it easier to add new file systems.
Types of File Systems
The Solaris operating environment supports three types of file systems:
Disk-based
Network-based
Virtual
To identify the file system type, see "Determining a File System's Type".
Disk-Based File Systems
Disk-based file systems are stored on physical media such as hard disks, CD-ROMs, and diskettes. Disk-based file systems can be written in different formats. The available formats are the following:
Disk-Based File System | Format Description |
|---|---|
UFS | UNIX file system (based on the BSD Fast File system that was provided in the 4.3 Tahoe release). UFS is the default disk-based file system for the Solaris operating environment. Before you can create a UFS file system on a disk, you must format the disk and divide it into slices. For information on formatting disks and dividing disks into slices, see Chapter 31, Managing Disks (Overview). |
HSFS | High Sierra, Rock Ridge, and ISO 9660 file system. High Sierra is the first CD-ROM file system. ISO 9660 is the official standard version of the High Sierra File System. The HSFS file system is used on CD-ROMs, and is a read-only file system. Solaris HSFS supports Rock Ridge extensions to ISO 9660, which, when present on a CD-ROM, provide all UFS file system features and file types, except for writability and hard links. |
PCFS | PC file system, which allows read and write access to data and programs on DOS-formatted disks that are written for DOS-based personal computers. |
UDF | The Universal Disk Format (UDF) file system, the industry-standard format for storing information on the optical media technology called DVD (Digital Versatile Disc or Digital Video Disc). |
Each type of disk-based file system is customarily associated with a particular media device, as follows:
UFS with hard disk
HSFS with CD-ROM
PCFS with diskette
UDF with DVD
These associations are not, however, restrictive. For example, CD-ROMs and diskettes can have UFS file systems created on them.
Network-Based File Systems
Network-based file systems can be accessed from the network. Typically, network-based file systems reside on one system, typically a server, and are accessed by other systems across the network.
With NFS, you can administer distributed resources (files or directories) by exporting them from a server and mounting them on individual clients. For more information, see "The NFS Environment".
Virtual File Systems
Virtual file systems are memory-based file systems that provide access to special kernel information and facilities. Most virtual file systems do not use file system disk space. However, the CacheFS file system uses a file system on the disk to contain the cache. Also, some virtual file systems, such as the temporary file system (TMPFS), use the swap space on a disk.
The CacheFS File System
The CacheFS™ file system can be used to improve performance of remote file systems or slow devices such as CD-ROM drives. When a file system is cached, the data that is read from the remote file system or CD-ROM is stored in a cache on the local system.
If you want to improve the performance and scalability of an NFS or CD-ROM file system, you should use the CacheFS file system. The CacheFS software is a general purpose caching mechanism for file systems that improves NFS server performance and scalability by reducing server and network load.
Designed as a layered file system, the CacheFS software provides the ability to cache one file system on another. In an NFS environment, CacheFS software increases the client per server ratio, reduces server and network loads, and improves performance for clients on slow links, such as Point-to-Point Protocol (PPP). You can also combine a CacheFS file system with the AutoFS service to help boost performance and scalability.
For detailed information about the CacheFS file system, see Chapter 40, Using The CacheFS File System (Tasks).
The Universal Disk Format (UDF) File System
The UDF file system is the industry-standard format for storing information on the DVD (Digital Versatile Disc or Digital Video Disc) optical media.
The UDF file system is provided as dynamically loadable, 32-bit and 64-bit modules, with system administration utilities for creating, mounting, and checking the file system on both SPARC and IA platforms. The Solaris UDF file system works with supported ATAPI and SCSI DVD drives, CD-ROM devices, and disk and diskette drives. In addition, the Solaris UDF file system is fully compliant with the UDF 1.50 specification.
The UDF file system provides the following features:
Ability to access the industry standard CD-ROM and DVD-ROM media when they contain a UDF file system
Flexibility in exchanging information across platforms and operating systems
A mechanism for implementing new applications rich in broadcast-quality video, high-quality sound along with the richness in interactivity using the DVD video specification based on UDF format
The following features are not included in the UDF file system:
Support for write-once media, CD-RW, and DVD-RAM, with either the sequential disk-at-once and incremental recording
UFS components such as quotas, ACLs, transaction logging, file system locking, and file system threads, which are not part of the UDF 1.50 specification
The UDF file system requires the following:
The Solaris 7 11/99, Solaris 8, or Solaris 9 releases
Supported SPARC or IA platforms
Supported CD-ROM or DVD-ROM device
The Solaris UDF file system implementation provides:
Support for industry-standard read/write UDF version 1.50
Fully internationalized file system utilities