Swap Space 5.1. What Is Swap Space; Adding Swap Space - Red Hat ENTERPRISE LINUX 5 - DEPLOYMENT Deployment Manual

Chapter 5.
Swap Space
5.1. What is Swap Space?
Swap space in Linux is used when the amount of physical memory (RAM) is full. If the system needs
more memory resources and the RAM is full, inactive pages in memory are moved to the swap space.
While swap space can help machines with a small amount of RAM, it should not be considered a
replacement for more RAM. Swap space is located on hard drives, which have a slower access time
than physical memory.
Swap space can be a dedicated swap partition (recommended), a swap file, or a combination of swap
partitions and swap files.
In years past, the recommended amount of swap space increased linearly with the amount of RAM in
the system. But because the amount of memory in modern systems has increased into the hundreds
of gigabytes, it is now recognized that the amount of swap space that a system needs is a function of
the memory workload running on that system. However, given that swap space is usually designated
at install time, and that it can be difficult to determine beforehand the memory workload of a system,
we recommend determining system swap using the following table.
Amount of RAM in the System
4GB of RAM or less
4GB to 16GB of RAM
16GB to 64GB of RAM
64GB to 256GB of RAM
256GB to 512GB of RAM
Table 5.1. Recommended System Swap Space
Important
File systems and LVM2 volumes assigned as swap space cannot be in use when being
modified. For example, no system processes can be assigned the swap space, as well as
no amount of swap should be allocated and used by the kernel. Use the free and cat /
proc/swaps commands to verify how much and where swap is in use.
The best way to achieve swap space modifications is to boot your system in rescue mode,
and then follow the instructions (for each scenario) in the remainder of this chapter. Refer
to the Red Hat Enterprise Linux Installation Guide for instructions on booting into rescue
mode. When prompted to mount the file system, select Skip.

5.2. Adding Swap Space

Sometimes it is necessary to add more swap space after installation. For example, you may upgrade
the amount of RAM in your system from 128 MB to 256 MB, but there is only 256 MB of swap space.
It might be advantageous to increase the amount of swap space to 512 MB if you perform memory-
intense operations or run applications that require a large amount of memory.
Recommended Amount of Swap Space
a minimum of 2GB of swap space
a minimum of 4GB of swap space
a minimum of 8GB of swap space
a minimum of 16GB of swap space
a minimum of 32GB of swap space
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