What are Disk Quotas?

[eUKShane]

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 Virtual Private Server can use. These quotas are known as per-VPS Hosting quotas or first-level quotas in virtuozzo. In addition, Virtuozzo enables the Virtual Private Sever administrator to limit disk space and the number of inodes that individual users and groups in that VPS Hosting can use. These quotas are called per-user and per-group quotas or second-level quotas in Virtuozzo.

By default, Virtuozzo has first-level quotas enabled (which is defined in the Virtuozzo global configuration file), whereas second-level quotas must be turned on for each Virtual Private Server separately (in the corresponding VPS Hosting configuration files). It is impossible to turn on second-level disk quotas for a Virtual Private Server if first-level disk quotas are off for that Virtual Private Server.

The disk quota block size in Virtuozzo is always 1024 bytes. It may differ from the block size of the underlying file system.

Virtuozzo keeps quota usage statistics and limits in

/var/vzquota/quota [VPS Hostingid] - 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 VPS Hosting usage. This means that when the disk space or inodes usage changes during the VPS Hosting operation,these statistics are not automatically synchronized with the quota file, the file just gets the “dirty� flag. They are synchronized only when the VPS Hosting is stopped or when the HN is shut down. After synchronization, the “dirty� flag is removed. If the Hardware Node has been incorrectly brought down (for example, the power switch was hit), the file remains “dirty�, and the quota is reinitialized on the next VPS Hosting startup. This operation may noticeably increase the Node startup time. Thus, it is highly recommended to shut down the Hardware Node properly.

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Best Regards,
UKShane
http://www.eukhost.com