Knowledge Base

High CPU wait, I/O and Load Average during backup or outbound migration on Plesk server

Symptoms

High CPU wait, I/O and Load Average, while the backup is generated in Plesk or outbound migration is performed.
Sites may show 504 Gateway Timeout error.

Cause

/usr/bin/pigz and/or /bin/tar consumes high CPU resource during the backup process as it is involved in the backup compress process. This applies to Plesk versions lower than 18.0.40 because starting from 18.0.40 Plesk uses ZSTD compression.

Resolution

There are three possible solutions to reduce the server load during backup process at Tools & Settings > Backup Manager > Settings:

Run scheduled backup processes with low priority
Run all backup processes with low priority. Since Plesk Obsidian 18.0.40 it is possible to set the compression level and IO priority:
Do not compress backup files (this way the backup size will be larger, but load average will be less as pigz process that is involved in the backup compress process will be skipped).

These options launch pigz and tar with nice.

Note: these options increase the backup time. Other server tasks will not be affected. If there is a highly-loaded domain on a server that takes a lot of server resources, re-schedule the time to start a backup to the night when the number of visitors to the site is less.