System Administration Guide: Devices and File Systems

Planning for Swap Space

The most important factors in determining swap space size are the requirements of the system's software applications. For example, large applications such as computer-aided design simulators, database management products, transaction monitors, and geologic analysis systems can consume as much as 200–1000 MB of swap space.

Consult your application vendors for swap space requirements for their applications.

If you are unable to determine swap space requirements from your application vendors, use the following general guidelines based on your system type to allocate swap space.

System Type	Swap Space Size	Dedicated Dump Device Size
System with about 4 GB of physical memory	1 GB	1 GB
Mid-range server with about 8 GB of physical memory	2 GB	2 GB
High-end server with about 16 to 128 GB of physical memory	4 GB	4 GB
High-end server with more than 128 GB of physical memory	1/4 of physical memory size	1/4 of physical memory size

Note –

Crash dump content is compressed so the dump device does not have to be the same size as physical memory. By default, the dump content value is set to kernel pages. However, if the dump content value is set to dump all memory pages, then consider increasing the dump size to half the size of physical memory or more.

Allocating Swap Space for UFS-Based Systems

In addition to preceding general guidelines, consider allocating swap space or disk space for a UFS-based system for the following:

A dedicated dump device.
The /var/crash directory. The default system crash dump content is kernel memory pages only and the dump is compressed before it is written. Consider sizing this directory to the size of the dump device unless you attend to keep several system crash dumps.
Determine whether large applications (such as compilers) will be using the /tmp directory. Then, allocate additional swap space to be used by TMPFS. For information about TMPFS, see Swap Space and the TMPFS File System.

Allocating Swap Space for ZFS-Based Systems

During an initial installation of a ZFS root file system or a Solaris Live Upgrade from a UFS file system to a ZFS root file system, a swap area is automatically created on a ZFS volume in the ZFS root pool, generally in the 512 MB to 2 GB range. In the case of a UFS to ZFS migration by using Solaris Live Upgrade, a swap volume is created based on the sizes of existing swap areas.

In a ZFS root pool, swap devices are not pre-allocated to fixed-size slices, so it is fairly easy to modify the swap size later.

After you assess the swap requirements of your applications, you can use the default swap size or adjust the swap volume size during an initial installation or after the installation, if necessary.

During an initial installation, the default dump volume size is calculated by the kernel based on dumpadm information and the size of physical memory. During a Live Upgrade migration from a UFS root file system to a ZFS root file system, the default dump volume size is set to half the size of physical memory, between 512 MB and 2 GB, in the ZFS BE.

In a ZFS environment, file systems consume space from the pool so the /var/crash directory consumes what it needs depending on how many crash dumps are saved.