Solaris File System Types

Objective:

Describe the purpose, features, and functions of disk-based, networked, and pseudo file systems in a Solaris operating environment, and explain the differences among these file system types.

Solaris file systems can be put into three categories: disk-based, network-based, and virtual.

Disk-Based File Systems

Disk-based file systems reside on the system's local disk. As of this writing, the following are four types of disk-based file systems found in Solaris 10:

UFS (Unix File System) The Unix file system, which is based on the BSD FFS Fast file system (the traditional Unix file system). The UFS is the default disk-based file system used in Solaris.
HSFS (High Sierra File System) The High Sierra and ISO 9660 file system, which supports the Rock Ridge extensions. The HSFS file system is used on CD-ROMs and is a read-only file system.
PCFS (PC File System) The PC file system, which allows read/write access to data and programs on DOS-formatted disks written for DOS-based personal computers.
UDF (Universal Disk Format) The Universal Disk Format file system. UDF is the new industry-standard format for storing information on optical media technology called DVD (digital versatile disc).
Not in Solaris 10 as of this writing, but worth noting is the zettabyte file system (ZFS), scheduled for a future Solaris 10 update, incorporating advanced data security and protection features, eliminating the need for fsck or other recovery mechanisms. By redefining file systems as virtualized storage, Solaris ZFS will enable virtually unlimited scalability.

Network-Based File Systems

Network-based file systems are file systems accessed over the network. Typically, they reside on one system and are accessed by other systems across the network.

The network file system (NFS) or remote file systems are file systems made available from remote systems. NFS is the only available network-based file system bundled with the Solaris operating environment. NFS is discussed in detail in Chapter 9, "Virtual File Systems, Swap Space, and Core Dumps."

Virtual File Systems

Virtual file systems, previously called pseudo file systems, are virtual or memory-based file systems that create duplicate paths to other disk-based file systems or provide access to special kernel information and facilities. Most virtual file systems do not use file system disk space, although a few exceptions exist. Cache file systems, for example, use a disk-based file system to contain the cache.

Some virtual file systems, such as the temporary file system, might use the swap space on a physical disk. The following is a list of some of the more common types of virtual file systems:

SWAPFS (Swap File System) A file system used by the kernel for swapping. Swap space is used as a virtual memory storage area when the system does not have enough physical memory to handle current processes.
PROCFS (Process File System) The Process File System resides in memory. It contains a list of active processes, by process number, in the /proc directory. Commands such as ps use information in the /proc directory. Debuggers and other development tools can also access the processes' address space by using file system calls.
LOFS (Loopback File System) The Loopback File System lets you create a new virtual file system, which can provide access to existing files using alternate pathnames. Once the virtual file system is created, other file systems can be mounted within it, without affecting the original file system.
CacheFS (Cache File System) The Cache File System lets you use disk drives on local workstations to store frequently used data from a remote file system or CD-ROM. The data stored on the local disk is the cache.
TMPFS (Temporary File System) The Temporary File System uses local memory for file system reads and writes. Because TMPFS uses physical memory and not the disk, access to files in a TMPFS is typically much faster than to files in a UFS. Files in the temporary file system are not permanent; they are deleted when the file system is unmounted and when the system is shut down or rebooted. TMPFS is the default file system type for the /tmp directory in the SunOS system software. You can copy or move files into or out of the /tmp directory just as you would in a UFS /tmp. When memory is insufficient to hold everything in the temporary file system, the TMPFS uses swap space as a temporary backing store, as long as adequate swap space is present.
MNTFS The MNTFS type maintains information about currently mounted file systems. MNTFS is described later in this chapter.
CTFS (Contract File System) The CTFS is associated with the /system/contract directory and is the interface for creating, controlling, and observing contracts. The service management facility (SMF) uses process contracts (a type of contract) to track the processes which compose a service.
DEVFS (Device file System) The DEVFS is used to manage the namespace of all devices on the system. This file system is used for the /devices directory. The devfs file system is new in Solaris 10 and increases system boot performance because only device entries that are needed to boot the system are attached. New device entries are added as the devices are accessed.
FDFS (File Descriptor File System) The FDFS provides explicit names for opening files by using file descriptors.
OBJFS (Object File System) The OBJFS (object) file system describes the state of all modules currently loaded by the kernel. This file system is used by debuggers to access information about kernel symbols without having to access the kernel directly .