QoS classes

A QoS class is a logical grouping of file system objects that are managed as a single entity for QoS purposes.

System classes

The QoS system classes are predefined objects that control internal file system operations. System classes can be further classified as follows.
Standard system classes
The three standard system classes are maintenance, miscellaneous, and other.
maintenance class

The maintenance class is assigned to long-running, I/O-intensive IBM Storage Scale maintenance commands such as mmadddisk, mmdeldisk, mmfsck, mmrestripefs, and others. For a full list of the IBM Storage Scale maintenance commands and their default classes, see Table 1.

misc class

The misc class is a special high-priority class that is reserved for critical file system operations. This QoS system class is automatically assigned to log management operations, metadata read and write operations, and other management tasks that are essential for maintaining file system integrity.

other class

The other class is assigned to all I/O that is not assigned to the maintenance, miscellaneous, or any user-defined class. It is the default catchall class.

Note:
  • When QoS is enabled for a file system, default monitoring throttles are automatically created for the maintenance, misc, and other classes, which makes it possible to observe the I/O limits for each respective class.
  • You cannot create a finite throttle for the misc class. Only the default monitoring throttle is permitted.

For best practices and workflows, see QoS deployment guidelines and Workflows for QoS classes.

DQR system classes
In addition to the three standard system classes described in System classes, QoS provides two built-in classes to control advanced QoS functions: dqr-all-sharing and dqr-fs-pool-limit.
dqr-all-sharing class

The dqr-all-sharing class is used to configure class sharing across multiple user-defined classes.

For more information, see DQR class sharing.

dqr-fs-pool-limit class

The dqr-fs-pool-limit class is used to configure aggregate per-pool limits to a file system.

For more information, see File-system-level QoS.

User classes: fileset-level QoS

QoS user classes provide the capability to regulate I/O access at the fileset level. Filesets can be associated with functional groups, such as departments, projects, or teams. By assigning differentiated limits at the class level, you can effectively create class-based performance tiers, thereby protecting high-priority workloads from resource contention and noisy neighbors.

For more information on the workflow, see Workflow for QoS user classes. For information about how to deploy performance tiers, see Example 1: Performance tiers creation.

Note:
  • A fileset can be bound to only one user class. A fileset cannot be bound to a system class.
  • A user class can have multiple filesets that are bound to it.
  • A user class must have at least one fileset that is bound to it before a throttle can be created for it.
  • I/O for a fileset that is not associated with a user class, or for which no throttle exists, is assigned to the system other class.
  • No limit exists for the number of user classes, other than limits imposed by operating system resources.
  • No limit exists for the number of filesets that can be associated with a user class, other than limits imposed by operating system resources.