Storage Foundation 7.4.1 Administrator's Guide - Linux

Placement classes

A placement class is a SmartTier attribute of a given volume in a volume set of a multi-volume file system. This attribute is a character string, and is known as a volume tag. A volume can have different tags, one of which can be the placement class. The placement class tag makes a volume distinguishable by SmartTier.

Volume tags are organized as hierarchical name spaces in which periods separate the levels of the hierarchy . By convention, the uppermost level in the volume tag hierarchy denotes the Storage Foundation component or application that uses a tag, and the second level denotes the tag's purpose. SmartTier recognizes volume tags of the form vxfs.placement_class.class_name. The prefix vxfs identifies a tag as being associated with VxFS. The placement_class string identifies the tag as a file placement class that SmartTier uses. The class_name string represents the name of the file placement class to which the tagged volume belongs. For example, a volume with the tag vxfs.placement_class.tier1 belongs to placement class tier1. Administrators use the vxassist command to associate tags with volumes.

See the vxassist(1M) manual page.

SmartTier policy rules specify file placement in terms of placement classes rather than in terms of individual volumes. All volumes that belong to a particular placement class are interchangeable with respect to file creation and relocation operations. Specifying file placement in terms of placement classes rather than in terms of specific volumes simplifies the administration of multi-tier storage.