System Administration Guide: Devices and File Systems

UFS File System

See the following sections for details about the UFS file system.

UFS File System Features

UFS is the default disk-based file system in Solaris OS. Most often, when you administer a disk-based file system, you are administering UFS file systems. UFS provides the following features.

UFS Feature 


Extended fundamental types (EFT) 

Provides 32-bit user ID (UID), group ID (GID), and device numbers.

Large file systems 

Allows files of about 1 terabyte in size in a file system that can be up to 16 terabytes in size. You can create a multiterabyte UFS file system on a disk with an EFI disk label.


UFS logging bundles the multiple metadata changes that comprise a complete UFS operation into a transaction. Sets of transactions are recorded in an on-disk log and are applied to the actual UFS file system's metadata. 

Multiterabyte file systems 

A multiterabyte file system enables creation of a UFS file system up to approximately 16 terabytes of usable space, minus approximately one percent overhead

State flags 

Shows the state of the file system: clean, stable, active, logging, or unknown. These flags eliminate unnecessary file system checks. If the file system is “clean,” “stable,” or “logging,” file system checks are not run.

For detailed information about the UFS file system structure, see Chapter 23, UFS File System (Reference).

Planning UFS File Systems

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

For information on default file system parameters as well as procedures for creating new UFS file systems, see Chapter 18, Creating UFS, TMPFS, and LOFS File Systems (Tasks).

64-bit: Support of Multiterabyte UFS File Systems

This Solaris release provides support for multiterabyte UFS file systems on systems that run a 64-bit Solaris kernel.

Previously, UFS file systems were limited to approximately 1 terabyte on both 64-bit and 32-bit systems. All UFS file system commands and utilities have been updated to support multiterabyte UFS file systems.

For example, the ufsdump command has been updated with a larger block size for dumping large UFS file systems:

# ufsdump 0f /dev/md/rdsk/d97 /dev/md/rdsk/d98
    DUMP: Date of this level 0 dump: Fri Oct 10 17:22:13 2008
    DUMP: Date of last level 0 dump: the epoch
    DUMP: Dumping /dev/md/rdsk/d97 to /dev/md/rdsk/d98
    DUMP: Mapping (Pass I) [regular files]
    DUMP: Mapping (Pass II) [directories]
    DUMP: Writing 32 Kilobyte records
    DUMP: Estimated 17439410 blocks (8515.34MB).
    DUMP: Dumping (Pass III) [directories]
    DUMP: Dumping (Pass IV) [regular files]

Administering UFS file systems that are less than 1 terabyte remains the same. No administration differences exist between UFS file systems that are less than one terabyte and file systems that are greater than 1 terabyte.

You can initially create a UFS file system that is less than 1 terabyte and specify that it can eventually be expanded into a multiterabyte file system by using the newfs -T option. This option sets the inode and fragment density to scale appropriately for a multiterabyte file system.

Using the newfs -T option when you create a UFS file system less than 1 terabyte on a system running a 32-bit kernel enables you to eventually expand this file system by using the growfs command when you boot this system under a 64-bit kernel. For more information, see newfs(1M).

You can use the fstyp -v command to identify whether a UFS file system has multiterabyte support by checking the following value in the magic column:

# /usr/sbin/fstyp -v /dev/md/rdsk/d3 | head -5
magic   decade  format  dynamic time    Thu Jul 17 11:15:36 2008

A UFS file system with no multiterabyte support has the following fstyp output:

# /usr/sbin/fstyp -v /dev/md/rdsk/d0 | head -5
magic   11954   format  dynamic time    Thu Jul 17 12:43:29 MDT 2008

You can use the growfs command to expand a UFS file system to the size of the slice or the volume without loss of service or data. For more information, see growfs(1M).

Two new related features are multiterabyte volume support with the EFI disk label and multiterabyte volume support with Solaris Volume Manager. For more information, see EFI Disk Label and the Solaris Volume Manager Administration Guide.

Features of Multiterabyte UFS File Systems

Multiterabyte UFS file systems include the following features:

Limitations of Multiterabyte UFS File Systems

Limitations of multiterabyte UFS file systems are as follows:

Where to Find Multiterabyte UFS Tasks

Use these references to find step-by-step instructions for working with multiterabyte UFS file systems.

Multiterabyte UFS Task 

For More Information 

Create multiterabyte UFS file systems 

How to Create a Multiterabyte UFS File System

How to Expand a Multiterabyte UFS File System

How to Expand a UFS File System to a Multiterabyte UFS File System

Create a multiterabyte UFS snapshot 

Example 26–2

Troubleshoot multiterabyte UFS problems 

Troubleshooting Multiterabyte UFS File System Problems

UFS Logging

UFS logging bundles the multiple metadata changes that comprise a complete UFS operation into a transaction. Sets of transactions are recorded in an on-disk log. Then, they are applied to the actual UFS file system's metadata.

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. A system crash might interrupt system calls and introduces inconsistencies into a UFS file system.

UFS logging provides two advantages:

Logging is enabled by default for all UFS file systems, except under the following conditions:

In previous Solaris releases, you had to manually enable UFS logging.

Keep the following issues in mind when using UFS logging:

The UFS transaction log has the following characteristics:

If you need to enable UFS logging, specify the -o logging option with the mount command in the /etc/vfstab file or when you manually mount the file system. Logging can be enabled on any UFS file system, including the root (/) file system. Also, the fsdb command has new debugging commands to support UFS logging.

In some operating systems, a file system with logging enabled is known as a journaling file system.

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 26, Using UFS Snapshots (Tasks) for more information.

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 that occurs when raw devices are accessed. 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 it can enable UFS direct I/O in its 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).