Chapter 17. Managing Tiering

Tiering refers to automatic classification and movement of data based on the user I/O access. The tiering feature continuously monitors the workload, identifies hotspots by measuring and analysing the statistics of the activity, and places the frequently accessed data on to the highest performance hot tier (such as solid state drives (SSDs)), and inactive data to the lower performing cold tier (such as Spinning disks) all without I/O interruption. With tiering, data promotion and auto-rebalancing address performance while cold demotion works to address capacity.

Tiering monitors and identifies the activity level of the data and auto rebalances the active and inactive data to the most appropriate storage tier. Moving data between tiers of hot and cold storage is a computationally expensive task. To address this, Red Hat Gluster Storage supports automated promotion and demotion of data within a volume in the background so as to minimize impact on foreground I/O. Data becomes hot or cold based on the rate at which it is accessed. If access to a file increases, it moves, or retains its place in the hot tier. If the file is not accessed for a while, it moves, or retains it place in the cold tier. Hence, the data movement can happen in either direction which is based totally on the access frequency.

Different sub-volume types act as hot and cold tiers and data is automatically assigned or reassigned a “temperature” based on the frequency of access. Red Hat Gluster Storage allows attaching fast performing disks as hot tier, uses the existing volume as cold tier, and these hot tier and cold tier forms a single tiered volume. For example, the existing volume may be distributed dispersed on HDDs and the hot tier could be distributed-replicated on SSDs.