Qgroups

Qgroups, short for quota groups, are a ZFS feature designed to provide fine-grained storage accounting and enforcement of quotas and reservations across multiple datasets. A qgroup is a logical entity that tracks space usage for a set of ZFS datasets and can enforce limits on that usage. Qgroups are organized in a hierarchical tree that reflects the dataset namespace, with quotas and reservations applied at the qgroup level to govern the total space that its member datasets may consume.

The core idea is to enable resource isolation and fair sharing in environments that host multiple datasets, such as multi-tenant storage pools or virtualization setups. Each dataset is associated with one or more qgroups, and the usage reported for a qgroup represents the aggregate space used by its member datasets and their descendants. Quotas (limits) restrict how much space the qgroup may use, while reservations guarantee a minimum amount of space for the qgroup.

Snapshots and clones are included in qgroup accounting, so space occupied by historical data is considered in the total usage. This makes qgroups a robust mechanism for enforcing constraints in environments where data growth and retention policies vary across tenants or projects.

Administrators manage qgroups through ZFS management tools, creating qgroups, assigning datasets to them, and configuring quotas and reservations. Monitoring features provide visibility into per-qgroup usage to help with capacity planning and policy enforcement.

Use cases include multi-tenant storage services, virtual machine or container environments, and cloud storage platforms where predictable budgeting and isolation of storage resources are important. Qgroups aim to balance efficient storage utilization with tenant isolation and administrative control.