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 like Solid State Drives (SSDs) and the base pool will be comprised of the slower storage devices like 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 yet still maintain a good level of performance of frequently accessed data.
In this chapter, we will cover the following topics:
- How Cephs tiering functionality works
- What are good use cases for tiering
- How to configure two pools into a tier
- Cover 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 required features that made tiering usable.