Swap space on cloud servers

  • Last updated on: 2019-01-31
  • Authored by: Rackspace Community

As of October 28, 2013, cloud servers built by using our base Linux® images are created without a dedicated swap partition and with swappiness (a measure of how the Linux kernel tries to use swap memory) set to 0. Any Linux cloud servers that you have built from older base images or server images retain any swap partition with which the images were originally created.

What is swap space?

Swap space is space on the hard disk that is reserved for use as virtual memory. When a cloud server runs out of memory, the Linux kernel moves inactive processes into swap space to make room for active ones in working memory. How aggressively your cloud server uses swap space is determined by the value for swappiness, which ranges from 0 to 100. A setting of 100 aggressively moves processes, while a setting of 0 swaps only to avoid an out-of-memory condition.

Why remove swap space?

In a multitenant cloud environment, certain resources are shared among customers. In the case of swap, the key resource that sharing affects is disk IOPS. IOPS stands for input/output operations per second, which is the number of read and write operations performed on the disk per second. When an application performs any sort of read or write operation on the physical hard disks, the application consumes disk IOPS.

If cloud servers that are running on the same physical host run more processes than their allotted random access memory (RAM), they begin to use swap space heavily. When this occurs, a large portion of the available disk IOPS pool is consumed, creating the noisy neighbor effect in which other virtual machines can monopolize the disk and affect your performance.

To provide the best service and consistent performance and to align with industry standard practice, we have removed the swap partition that we previously gave to each virtual machine by default. We believe that this change enables a better customer experience.

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