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System Administration Guide: Devices and File Systems     Oracle Solaris 10 8/11 Information Library
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Document Information

About This Book

1.  Managing Removable Media (Overview)

2.  Managing Removable Media (Tasks)

3.  Accessing Removable Media (Tasks)

4.  Writing CDs and DVDs (Tasks)

5.  Managing Devices (Overview/Tasks)

6.  Dynamically Configuring Devices (Tasks)

7.  Using USB Devices (Overview)

8.  Using USB Devices (Tasks)

9.  Using InfiniBand Devices (Overview/Tasks)

10.  Managing Disks (Overview)

11.  Administering Disks (Tasks)

12.  SPARC: Setting Up Disks (Tasks)

13.  x86: Setting Up Disks (Tasks)

14.  Configuring Oracle Solaris iSCSI Targets and Initiators (Tasks)

15.  The format Utility (Reference)

16.  Managing File Systems (Overview)

17.  Creating and Mounting File Systems (Tasks)

18.  Using The CacheFS File System (Tasks)

19.  Configuring Additional Swap Space (Tasks)

About Swap Space

Swap Space and Virtual Memory

Swap Space and the TMPFS File System

Swap Space as a Dump Device

Swap Space and Dynamic Reconfiguration

Configuring Swap Space in a SAN Environment

How Do I Know If I Need More Swap Space?

Swap-Related Error Messages

TMPFS-Related Error Messages

How Swap Space Is Allocated

Swap Areas and the /etc/vfstab File

Planning for Swap Space

Allocating Swap Space for UFS-Based Systems

Allocating Swap Space for ZFS-Based Systems

Monitoring Swap Resources

Adding More Swap Space

Creating a Swap File in a UFS Root Environment

mkfile Command

How to Create a Swap File and Make It Available in UFS Root Environment

Adding or Changing Swap Space in an Oracle Solaris ZFS Root Environment

How to Add Swap Space in an Oracle Solaris ZFS Root Environment

Removing a Swap File From Use

How to Remove Unneeded Swap Space in UFS Root Environment

How to Remove a Swap Volume in a ZFS Root Environment

20.  Checking UFS File System Consistency (Tasks)

21.  UFS File System (Reference)

22.  Backing Up and Restoring UFS File Systems (Overview)

23.  Backing Up UFS Files and File Systems (Tasks)

24.  Using UFS Snapshots (Tasks)

25.  Restoring UFS Files and File Systems (Tasks)

26.  UFS Backup and Restore Commands (Reference)

27.  Copying Files and File Systems (Tasks)

28.  Managing Tape Drives (Tasks)


About Swap Space

You should understand the features of the SunOS swap mechanism to determine the following:

Swap Space and Virtual Memory

Oracle Solaris OS software and application software can use some disk space for temporary storage rather than for file systems. The reserved area of the disk is called swap space. Swap space is used as virtual memory storage areas when the system does not have enough physical memory to handle current processes. In a UFS root file system, the disk space reserved for swap is a disk slice. In a ZFS root file system, the disk space reserved for swap is a ZFS volume.

The virtual memory system maps physical copies of files on disk to virtual addresses in memory. Physical memory pages that contain the data for these mappings can be backed by regular files in the file system, or by swap space. If the memory is backed by swap space it is referred to as anonymous memory because no identity is assigned to the disk space that is backing the memory.

The Oracle Solaris OS uses the concept of virtual swap space, a layer between anonymous memory pages and the physical storage (or disk-backed swap space) that actually back these pages. A system's virtual swap space is equal to the sum of all its physical (disk-backed) swap space plus a portion of the currently available physical memory.

Virtual swap space has these advantages:

Swap Space and the TMPFS File System

The TMPFS file system is activated automatically in the Oracle Solaris environment by an entry in the /etc/vfstab file. The TMPFS file system stores files and their associated information in memory (in the /tmp directory) rather than on disk, which speeds access to those files. This feature results in a major performance enhancement for applications such as compilers and DBMS products that use /tmp heavily.

The TMPFS file system allocates space in the /tmp directory from the system's swap resources. This feature means that as you use up space in the /tmp directory, you are also using up swap space. So, if your applications use the /tmp directory heavily and you do not monitor swap space usage, your system could run out of swap space.

Do use the following if you want to use TMPFS, but your swap resources are limited:

Swap Space as a Dump Device

A dump device is usually disk space that is reserved to store system crash dump information. By default, a system's dump device is configured to be a swap slice in a UFS root environment. If possible, you should configure an alternate disk partition as a dedicated dump device instead to provide increased reliability for crash dumps and faster reboot time after a system failure. You can configure a dedicated dump device by using the dumpadm command. For more information, see Chapter 17, Managing System Crash Information (Tasks), in System Administration Guide: Advanced Administration.

In a ZFS root environment, swap and dump are configured as separate ZFS volumes. The advantages to this model are as follows:

For more information about using ZFS swap and dump devices, see ZFS Support for Swap and Dump Devices in Oracle Solaris ZFS Administration Guide.

If you are using a volume manager to manage your disks in a UFS environment, such as Solaris Volume Manager, do not configure your dedicated dump device to be under its control. You can keep your swap areas under Solaris Volume Manager's control, which is a recommended practice. However, for accessibility and performance reasons, configure another disk as a dedicated dump device outside of Solaris Volume Manager's control.

Swap Space and Dynamic Reconfiguration

A good practice is to allocate enough swap space to support a failing CPU or system board during dynamic reconfiguration. Otherwise, a CPU or system board failure might result in your host or domain rebooting with less memory.

Without having this additional swap space available, one or more of your applications might fail to start due to insufficient memory. This problem would require manual intervention either to add additional swap space or to reconfigure the memory usage of these applications.

If you have allocated additional swap space to handle a potential loss of memory on reboot, all of your intensive applications might start as usual. This means the system will be available to the users, perhaps possibly slower due to some additional swapping.

For more information, see your hardware dynamic reconfiguration guide.

Configuring Swap Space in a SAN Environment

Review the following points to determine whether you might configure swap space on a network-connected disk, such as in a SAN environment: