Chapter 37 Managing File Systems (Overview)

The management of file systems is one of your most important system administration tasks.

This is a list of the overview information in this chapter.

• What's New in File Systems?

• Where to Find File System Management Tasks

• Overview of File Systems

• Types of File Systems

• Commands for File System Administration

• The Default Solaris File Systems

• Swap Space

• The UFS File System

• Mounting and Unmounting File Systems

• Determining a File System's Type

What's New in File Systems?

This section describes new file system features in the Solaris 9 release.

Extended File Attributes

The UFS, NFS, and TMPFS file systems have been enhanced to include extended file attributes, which enable application developers to associate specific attributes to a file. For example, a developer of a windowing system file management application might choose to associate a display icon with a file. Extended file attributes are logically represented as files within a hidden directory that is associated with the target file.

You can use the runat command to add attributes and execute shell commands in the extended attribute name space, which is a hidden attribute directory that is associated with the specified file.

To use the runat command to add attributes to a file, you first have to create the attributes file.

$ runat filea cp /tmp/attrdata attr.1

Then, use the runat command to list the attributes of a file.

$ runat filea ls -l

For more information, see the runat(1) man page.

Many Solaris file system commands have been modified to support file system attributes by providing an attribute-aware option that you can use to query, copy, or find file attributes. For more information, see the specific man page for each file system command.

UFS Snapshots

You can use the fssnap command to create a read-only snapshot of a file system. A snapshot is a file system's temporary image that is intended for backup operations.

See Chapter 47, Using UFS Snapshots (Tasks) for more information.

Improved UFS Direct I/O Concurrency

The performance of direct I/O, which is used by database applications to access unbuffered file system data, has been improved by allowing concurrent read and write access to regular UFS files. Previously, an operation that updated file data would lock out all other read or write accesses until the update operation was completed.

Concurrent writes are restricted to the special case of file rewrites. If the file is being extended, writing is single threaded as before. Generally, databases pre-allocate files and seldomly extend them thereafter. Therefore, the effects of this enhancement are evident during normal database operations.

The direct I/O improvements brings I/O bound database performance on a UFS file system to about 90% of raw partition access speeds. If the database is CPU bound or bus bandwidth bound, there might be no improvement.

Consider running your I/O database applications with direct I/O enabled if you are already using UFS to store database tables. Use your database administrative procedures to enable direct I/O, if possible. If there is no way to enable direct I/O through your database product, use the mount -forcedirectio option to enable direct I/O for each file system. Or, use the directio(3C) library call to enable direct I/O.

See mount_ufs(1M) or directio(3C) for more information.

Improved mkfs Performance

The mkfs command now has improve performance when you create file systems. Improved mkfs performance is often 10 times faster than in previous Solaris releases. Performance improvements occur on systems when you create both large and small file systems. However, the biggest performance improvements occur when creating file systems on systems with high-capacity disks or high-speed disks.

New labelit Options for UDF File Systems

The labelit command provides new options for use with Universal Disk Format (UDF) file systems. You can use the new labelit command options to identify the author name, organization, and contact information for a UDF volume.

There was no mechanism to update this information, which is part of general UDF file systems, in previous Solaris releases.

The new UDF specific options for the labelit command, specified with the -o option, are the following:

• lvinfo1 - Identifies the person who is creating the file system

• lvinfo2 - Identifies the organization that is responsible for creating the file system

• lvinfo3 - Identifies the contact information for media that contains the UDF file system

The maximum length for each option is 35 bytes.

For more information, see labelit_udfs(1M).

Where to Find File System Management Tasks

Use these references to find step-by-step instructions for the management of file systems.

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:

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^TM 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

Temporary File System

The temporary file system (TMPFS) uses local memory for file system reads and writes, which is typically much faster than a UFS file system. Using TMPFS can improve system performance by saving the cost of reading and writing temporary files to a local disk or across the network. For example, temporary files are created when you compile a program, and the operating system generates a lot of disk activity or network activity while manipulating these files. Using TMPFS to hold these temporary files can significantly speed up their creation, manipulation, and deletion.

Files in TMPFS file systems 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 Solaris operating environment. You can copy or move files into or out of the /tmp directory, just as you would in a UFS file system.

The TMPFS file system uses swap space as a temporary backing store. If a system with a TMPFS file system does not have adequate swap space, two problems can occur:

• The TMPFS file system can run out of space, just as regular file systems do.

• Because TMPFS allocates swap space to save file data (if necessary), some programs might not execute because of insufficient swap space.

For information about creating TMPFS file systems, see Chapter 38, Creating File Systems (Tasks). For information about increasing swap space, see Chapter 41, Configuring Additional Swap Space (Tasks).

The Loopback File System

The loopback file system (LOFS) lets you create a new virtual file system so that you can access files by using an alternative path name. For example, you can create a loopback mount of root (/) on /tmp/newroot, which will make the entire file system hierarchy look like it is duplicated under /tmp/newroot, including any file systems mounted from NFS servers. All files will be accessible either with a path name starting from root (/), or with a path name that starts from /tmp/newroot.

For information on how to create LOFS file systems, see Chapter 38, Creating File Systems (Tasks).

Process File System

The process file system (PROCFS) resides in memory and contains a list of active processes, by process number, in the /proc directory. Information in the /proc directory is used by commands like ps. Debuggers and other development tools can also access the address space of the processes by using file system calls.

Do not delete the files in the /proc directory. The deletion of processes from the /proc directory does not kill them. Remember, /proc files do not use disk space, so there is little reason to delete files from this directory.

The /proc directory does not require administration.

Additional Virtual File Systems

These additional types of virtual file systems are listed for your information. They do not require administration.

Commands for File System Administration

Most commands for file system administration have both a generic component and a file system–specific component. Whenever possible, you should use the generic commands, which call the file system–specific component. The following table lists the generic commands for file system administration, which are located in the /usr/sbin directory.

How File System Commands Determine the File System Type

The generic file system commands determine the file system type by following this sequence:

1. From the -F option, if supplied.

2. By matching a special device with an entry in the /etc/vfstab file (if special is supplied). For example, fsck first looks for a match against the fsck device field. If no match is found, it then checks the special device field.

3. By using the default specified in the /etc/default/fs file for local file systems and in the /etc/dfs/fstypes file for remote file systems.

Manual Pages for Generic and Specific Commands

Both the generic commands and specific commands have manual pages in the man Pages(1M): System Administration Commands. The manual page for the generic file system commands provide information about generic command options only. The manual page for a specific file system command has specific information about options for that file system. To look at a specific manual page, append an underscore and the abbreviation for the file system type to the generic command name. For example, to see the specific manual page for mounting a UFS file system, type the following:

$ man mount_ufs

The Default Solaris File Systems

The Solaris UFS file system is hierarchical, starting with the root directory (/) and continuing downwards through a number of directories. The Solaris installation process enables you to install a default set of directories and uses a set of conventions to group similar types of files together. The following table provides a summary of the default Solaris file systems.

The root (/) and /usr file systems are needed to run a system. Some of the most basic commands in the /usr file system (like mount) are included in the root (/) file system so that they are available when the system boots or is in single-user mode and /usr is not mounted. For more detailed information on the default directories for the root (/) and /usr file systems, see Chapter 43, UFS File System (Reference).

Swap Space

The Solaris operating environment uses some disk slices for temporary storage rather than for file systems. These slices are called swap slices, or swap space. Swap space is used as virtual memory storage areas when the system does not have enough physical memory to handle current processes.

Since many applications rely on swap space, you should know how to plan for, monitor, and add more swap space when needed. For an overview about swap space and instructions for adding swap space, see Chapter 41, Configuring Additional Swap Space (Tasks).

The UFS File System

UFS is the default disk-based file system in Solaris operating environment. Most often, when you administer a disk-based file system, you will be administering UFS file systems. UFS provides the following features:

For detailed information about the UFS file system structure, see Chapter 43, UFS File System (Reference).

UFS Logging

UFS logging is the process of storing transactions (changes that make up a complete UFS operation) in a log before the transactions are applied to the UFS file system. Once a transaction is stored, the transaction can be applied to the file system later.

At reboot, the system discards incomplete transactions, but applies the transactions for completed operations. The file system remains consistent because only completed transactions are ever applied. This consistency remains even when a system crashes, which normally interrupts system calls and introduces inconsistencies into a UFS file system.

UFS logging provides two advantages:

• Prevents file systems from becoming inconsistent, therefore eliminating the need to run the fsck command. And, because fsck checking can be bypassed, UFS logging reduces the time required to reboot a system if it crashes, or after an unclean halt (see What the fsck Command Checks and Tries to Repair for details on unclean halts).

• UFS logging can significantly reduce the boot time on systems with large file systems, which usually take a long time to read and verify with the fsck command.

The log created by UFS logging is continually flushed as it fills up. The log is flushed when the file system is unmounted or as a result of the lockfs -f command.

UFS logging is not enabled by default. To enable UFS logging, you must specify the -o logging option with the mount command in the /etc/vfstab file or when you mount the file system manually. The log is allocated from free blocks on the file system, and it is sized at approximately 1 Mbyte per 1 Gbyte of file system, up to a maximum of 64 Mbytes. Logging can be enabled on any UFS file system, including the root (/) file system. Also, the fsdb command now has new debugging commands to support UFS logging.

Planning UFS File Systems

When laying out file systems, you need to consider possible conflicting demands. Here are some suggestions:

• Distribute the work load as evenly as possible among different I/O systems and disk drives. Distribute the /export/home file system and swap space evenly across disks.

• Keep pieces of projects or members of groups within the same file system.

• Use as few file systems per disk as possible. On the system (or boot) disk, you should have three file systems: root (/), /usr, and swap space. On other disks, create one or, at most, two file systems; one being additional swap space, preferably. Fewer, roomier file systems cause less file fragmentation than many small, over-crowded file systems. Higher-capacity tape drives and the ability of the ufsdump command to handle multiple volumes make it easier to back up larger file systems.

• If you have some users who consistently create very small files, consider creating a separate file system with more inodes. However, most sites do not need to keep similar types of user files in the same file system.

For information on default file system parameters as well as procedures for creating new UFS file systems, see Chapter 38, Creating File Systems (Tasks).

UFS Direct Input/Output (I/O)

Direct I/O is intended to boost bulk I/O operations. Bulk I/O operations use large buffer sizes to transfer large files (larger than 256 Kbytes).

Using UFS direct I/O might benefit applications, such as database engines, that do their own internal buffering. Starting with the Solaris 8 1/01 release, UFS direct I/O has been enhanced to allow the same kind of I/O concurrency seen when accessing raw devices. Now you can get the benefit of file system naming and flexibility with very little performance penalty. Check with your database vendor to see if they can enable UFS direct I/O in their product configuration options.

Direct I/O can also be enabled on a file system by using the forcedirectio option to the mount command. Enabling direct I/O is a performance benefit only when a file system is transferring large amounts of sequential data.

When a file system is mounted with this option, data is transferred directly between a user's address space and the disk. When forced direct I/O is not enabled for a file system, data transferred between a user's address space and the disk is first buffered in the kernel address space.

The default behavior is no forced direct I/O on a UFS file system. For more information, see mount_ufs(1M).

Mounting and Unmounting File Systems

Before you can access the files on a file system, you need to mount the file system. When you mount a file system, you attach that file system to a directory (mount point) and make it available to the system. The root (/) file system is always mounted. Any other file system can be connected or disconnected from the root (/) file system.

When you mount a file system, any files or directories in the underlying mount point directory are unavailable as long as the file system is mounted. These files are not permanently affected by the mounting process, and they become available again when the file system is unmounted. However, mount directories are typically empty, because you usually do not want to obscure existing files.

For example, the following figure shows a local file system, starting with a root (/) file system and the sbin, etc, and opt subdirectories.

Figure 37–1 Sample root (/) File System

To access a local file system from the /opt file system that contains a set of unbundled products, you must do the following:

• First, you must create a directory to use as a mount point for the file system you want to mount, for example, /opt/unbundled.

• Once the mount point is created, you can mount the file system (by using the mount command), which makes all of the files and directories in /opt/unbundled available, as shown in the following figure.

For step-by-step instructions on how to mount file systems, see Chapter 39, Mounting and Unmounting File Systems (Tasks).

Figure 37–2 Mounting a File System

The Mounted File System Table

Whenever you mount or unmount a file system, the /etc/mnttab (mount table) file is modified with the list of currently mounted file systems. You can display the contents of this file with the cat or more commands, but you cannot edit it. Here is an example of an /etc/mnttab file:

$ more /etc/mnttab
/dev/dsk/c0t0d0s0  /  ufs rw,intr,largefiles,onerror=panic,suid,dev=2200000 938557523
/proc   /proc   proc    dev=3180000     938557522
fd      /dev/fd fd      rw,suid,dev=3240000     938557524
mnttab  /etc/mnttab     mntfs   dev=3340000     938557526
swap    /var/run        tmpfs   dev=1   938557526
swap    /tmp    tmpfs   dev=2   938557529
/dev/dsk/c0t0d0s7 /export/home ufs rw,intr,largefiles,onerror=panic,suid,dev=2200007 ...
$

The Virtual File System Table

It would be a very time-consuming and error-prone task to manually mount file systems every time you wanted to access them. To avoid this problem, the virtual file system table (the /etc/vfstab file) provides a list of file systems and how to mount them.

The /etc/vfstab file provides two important features:

• You can specify file systems to automatically mount when the system boots.

• You can mount file systems by using only the mount point name, because the /etc/vfstab file contains the mapping between the mount point and the actual device slice name.

A default /etc/vfstab file is created when you install a system, depending on the selections you make when installing system software. However, you can edit the /etc/vfstab file on a system whenever you want. To add an entry, the main information you need to specify is the device where the file system resides, the name of the mount point, the type of the file system, whether you want the file system to mount automatically when the system boots (by using the mountall command), and any mount options.

The following is an example of an /etc/vfstab file. Comment lines begin with #. This example shows an /etc/vfstab file for a system with two disks (c0t0d0 and c0t3d0).

$ more /etc/vfstab
#device         device          mount           FS      fsck   mount  mount
#to mount       to fsck         point           type    pass   at boot options
/dev/dsk/c0t0d0s0 /dev/rdsk/c0t0d0s0 /          ufs     1       no      -
/proc           -               /proc           proc    -       no      -
/dev/dsk/c0t0d0s1 -                -            swap    -       no      -
swap            -               /tmp            tmpfs   -       yes     -
/dev/dsk/c0t0d0s6 /dev/rdsk/c0t0d0s6 /usr       ufs     2       no      -
/dev/dsk/c0t3d0s7 /dev/rdsk/c0t3d0s7 /test      ufs     2       yes     -
$

In the preceding example, the last entry specifies that a UFS file system on the /dev/dsk/c0t3d0s7 slice will be automatically mounted on the /test mount point when the system boots. Note that, for root (/) and /usr, the mount at boot field value is specified as no, because these file systems are mounted by the kernel as part of the boot sequence before the mountall command is run.

For descriptions of each of the /etc/vfstab fields and information on how to edit and use the file, see Chapter 39, Mounting and Unmounting File Systems (Tasks).

The NFS Environment

NFS is a distributed file system service that can be used to share resources (files or directories) from one system, typically a server, with other systems on the network. For example, you might want to share third-party applications or source files with users on other systems.

NFS makes the actual physical location of the resource irrelevant to the user. Instead of placing copies of commonly used files on every system, NFS allows you to place one copy on one system's disk and let all other systems access it from the network. Under NFS, remote files are virtually indistinguishable from local ones.

A system becomes an NFS server if it has resources to share on the network. A server keeps a list of currently shared resources and their access restrictions (such as read/write or read-only access).

When you share a resource, you make it available for mounting by remote systems.

You can share a resource in these ways:

• By using the share or shareall command

• By adding an entry to the /etc/dfs/dfstab (distributed file system table) file and rebooting the system

For information on how to share resources, see Chapter 39, Mounting and Unmounting File Systems (Tasks). For a complete description of NFS, see “Managing Network File Systems (Overview)” in System Administration Guide: Resource Management and Network Services.

Automounting or AutoFS

You can mount NFS file system resources by using a client-side service called automounting (or AutoFS), which enables a system to automatically mount and unmount NFS resources whenever you access them. The resource remains mounted as long as you remain in the directory and are using a file. If the resource is not accessed for a certain period of time, it is automatically unmounted.

AutoFS provides the following features:

• NFS resources don't need to be mounted when the system boots, which saves booting time.

• Users don't need to know the root password to mount and unmount NFS resources.

• Network traffic might be reduced, since NFS resources are only mounted when they are in use.

The AutoFS service is initialized by the automount utility, which runs automatically when a system is booted. The automountd daemon runs continuously and is responsible for the mounting and unmounting of the NFS file systems on an as-needed basis. By default, the /home file system is is mounted by the automount daemon.

With AutoFS, you can specify multiple servers to provide the same file system. This way, if one of the servers is down, AutoFS can try to mount from another machine.

For complete information on how to set up and administer AutoFS, see System Administration Guide: IP Services.

Determining a File System's Type

You can determine a file system's type by using the following:

• The FS type field in the virtual file system table (/etc/vfstab file)

• The /etc/default/fs file for local file systems

• The /etc/dfs/fstypes file for NFS file systems

How to Determine a File System's Type

This procedure works whether the file system is mounted or not.

Determine a file system's type by using the grep command.

$ grep mount-point fs-table

Information for the mount point is displayed.

If you have the raw device name of a disk slice, you can use the fstyp command to determine a file system's type (if the disk slice contains a file system). For more information, see fstyp(1M).

Example—Determining a File System's Type

The following example uses the /etc/vfstab file to determine the type of the /export file system.

$ grep /export /etc/vfstab
/dev/dsk/c0t3d0s6   /dev/rdsk/c0t3d0s6  /export ufs   2       yes    -
$ 

The following example uses the /etc/mnttab file to determine the file system type of the currently mounted diskette (which was mounted by vold).

$ grep /floppy /etc/mnttab
/vol/dev/diskette0/unnamed_floppy   /floppy/unnamed_floppy  pcfs rw,
nohidden,nofoldcase,dev=16c0009      89103376
$