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Oracle Solaris Administration: Devices and File Systems     Oracle Solaris 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 Storage Devices With COMSTAR

15.  Configuring and Managing the Oracle Solaris Internet Storage Name Service (iSNS)

16.  The format Utility (Reference)

17.  Managing File Systems (Overview)

18.  Creating and Mounting File Systems (Tasks)

19.  Configuring Additional Swap Space (Tasks)

About Swap Space

Swap Space and Virtual Memory

Swap Space and the TMPFS File System

Swap Space and Dump Device Configuration

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 ZFS-Based Systems

Monitoring Swap Resources

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

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

20.  Copying Files and File Systems (Tasks)

21.  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 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 and Dump Device Configuration

A dump device is usually disk space that is reserved to store system crash dump information. When a system is installed, a ZFS swap volume and dump volume are created automatically. You can change a system's dump volume by using the dumpadm command. For more information, see Chapter 17, Managing System Crash Information (Tasks), in Oracle Solaris Administration: Common Tasks.

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 Managing Your ZFS Swap and Dump Devices in Oracle Solaris Administration: ZFS File Systems.

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: