"Oracle Solaris 11.3 文件系统管理指南"

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♦ ♦ ♦ C H A P T E R 2

Managing File Systems

This chapter describes how to create, mount, and unmount a file system. This chapter also

describes how to resolve UFS file system inconsistencies and errors.

This chapter contains the following topics:

■

“Creating a File System” on page 15

■

“Determining the Type of a File System” on page 22

■

“Mounting a File System” on page 23

■

“The Virtual File System Table” on page 26

■

“Unmounting a File System” on page 31

■

“Checking UFS File System Consistencies” on page 32

■

“Resolving UFS File System Inconsistencies” on page 36

Creating a File System

To create a new file system, you must format and label a disk or a storage device such as USB,

flash disk, or memory card. You can also create a file system spanning a whole device. Usually

volumes are provided by a volume manager such as Solaris volume manager (SVM). There are

no procedures to create network-based and virtual file systems.

For information about how to create a ZFS file system, see Managing ZFS File Systems in

Oracle Solaris 11.3.

Caution - While creating a new file system, ensure that you specify the correct device name. If

you specify an incorrect device name, the content in that device will be erased. This error might

cause the system to panic.

You can use the mkfs command to create a file system.

# mkfs -F type [-o parameters] raw_device [parameters]

Chapter 2 • Managing File Systems 15

Creating a File System

The logical block size is the size of the block that the UNIX kernel uses to read or write a file.

The logical block size is usually different from the physical block size. The physical block size

is usually 512 bytes, which is the size of the smallest block that a disk controller can read or

write. Logical block size is set to the page size of the system by default. The default logical

block size is 8192 bytes (8 KB) for UFS file systems. The UFS file system supports block sizes

of 4096 or 8192 bytes (4 or 8 KB). It is a best practice to set the logical block size to 8 KB.

To choose the best logical block size suitable for your system, you must consider both

performance and available space. For most UFS systems, an 8 KB file system provides the best

performance, offering a good balance between disk performance, and the use of space in the

primary memory and on the disk.

To increase efficiency, you can use a larger logical block size for file systems when most of the

files are large. Use a smaller logical block size for file systems when most of the files are small.

You can use the -c option with the newfs command on a file system to display a complete report

on the distribution of files by block size. However, the page size that is set when the file system

is created is probably the best size in most cases.

Fragment Size

The fragment size parameter can be set using the -f fragsize parameter with the newfs

command.

As files are created or expanded, they are allocated with disk space with either full logical

blocks or portions of logical blocks called fragments. When disk space is needed for a file,

full blocks are allocated first, and then one or more fragments of a block are allocated for the

remainder. For small files, allocation begins with fragments.

The ability to allocate fragments of blocks to files saves space by reducing fragmentation of

disk space that result from unused holes in blocks.

You define the fragment size when you create a UFS file system. The default fragment size is 1

KB. Each block can be divided into 1, 2, 4, or 8 fragments, which results in fragment sizes from

8192 bytes to 512 bytes (for 4 KB file systems only). The lower bound is actually tied to the

disk sector size, typically 512 bytes.

For multi-terabyte file systems, the fragment size must be equal to the file system block size.

When choosing a fragment size, consider the trade-off between space and time. A small

fragment size saves space, but requires more time to allocate. To increase storage efficiency, use

a larger fragment size for file systems when most of the files are large. Use a smaller fragment

size for file systems when most of the files are small.

18 Managing File Systems in Oracle Solaris 11.3 • October 2017

Creating a File System

Minimum Free Space

The minimum free space is the percentage of the total disk space that is held in reserve when

you create a file system. The default reserve is ((64 MB/partition size) * 100), rounded down to

the nearest integer and limited between 1 percent and 10 percent, inclusively.

Free space is important because file access becomes less efficient when a file system becomes

full. As long as an adequate amount of free space exists, UFS file systems operate efficiently.

When a file system becomes full, using the available user space, only root can access the

reserved free space.

Commands such as df reports the percentage of space that is available to users, excluding the

percentage allocated as the minimum free space. When the command reports that more than 100

percent of the disk space in the file system is in use, some of the reserve space has been used by

root.

If you impose quotas on users, the amount of space available to them does not include the

reserved free space. You can change the value of the minimum free space for an existing file

system using the tunefs command.

Optimization Type

The optimization type (-o option) is set to either space or time.

space

When you select space optimization, disk blocks are allocated to

minimize fragmentation and disk use is optimized.

time

When you select time optimization, disk blocks are allocated as quickly

as possible, with less emphasis on their placement. When sufficient free

space exists, allocating disk blocks is relatively easy, without resulting in

too much fragmentation. The default is time.

You can change the value of the optimization type parameter for an existing file system by

using the tunefs command. For more information, see the tunefs(1M) man page.

Number of Inodes

The number of bytes per inode specifies the density of inodes in the file system. The number

of bytes is divided into the total size of the file system to determine the number of inodes to

create. Once the inodes are allocated, you cannot change the number without re-creating the file

system.

Chapter 2 • Managing File Systems 19

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