What are Disk Quotas?

Disk quotas enable system administrators to control the size of Linux file systems by limiting the amount of disk space and the number of inodes a Container can use. These quotas are known as per-Container quotas or first-level quotas in Parallels Server Bare Metal. In addition, the Parallels Server Bare Metal software enables the Container administrator to limit disk space and the number of inodes that individual users and groups in that Container can use. These quotas are called per-user and per-group quotas or second-level quotas.

By default, first-level quotas on your server are enabled (which is defined in the /etc/vz/vz.conf configuration file), whereas second-level quotas must be turned on for each Container separately (in the corresponding Container configuration files). It is impossible to turn on second-level disk quotas for a Container if first-level disk quotas are off for that Container.

Parallels Server Bare Metal keeps quota usage statistics and limits in /var/vzquota/quota.< CT_ID > - a special quota file. The quota file has a special flag indicating whether the file is “dirty”. The file becomes dirty when its contents become inconsistent with the real Container usage. This means that when the disk space or inodes usage changes during the Container operation, these statistics are not automatically synchronized with the quota file, the file just gets the “dirty” flag. They are synchronized only when the Container is stopped or when the server is shut down. After synchronization, the “dirty” flag is removed. If the server has been incorrectly brought down (for example, the power switch was hit), the file remains “dirty”, and the quota is re-initialized on the next Container startup. This operation may noticeably increase the server startup time. Thus, it is highly recommended to shut down the server properly.