The tiering functionality in Ceph allows you to overlay one RADOS pool over another and let Ceph intelligently promote and evict objects between them. In most configurations, the top-level pool will be comprised of fast storage devices such as Solid State Drives (SSDs) and the base pool will be comprised of slower storage devices such as Serial ATA (SATA) or Serial Attached SCSI (SAS) disks. If the working set of your data is of a comparatively small percentage, then this allows you to use Ceph to provide high capacity storage but still maintain a good level of performance of frequently accessed data.
In this chapter, we will cover the following topics:
- How Ceph's tiering functionality works
- What good use cases for tiering are
- How to configure two pools into a tier
- Various tuning options available for tiering
It's recommended that you should be running at least the Jewel release of Ceph if you wish to use the tiering functionality. Previous releases were lacking a lot of features that made tiering usable.