Not All Data Deserves Fast Disk
Most data is accessed a lot when new and almost never after a while. Tiered storage matches the cost of the medium to the value of the access by moving data through hot, warm, and cold tiers over its lifetime.
The Tiers
- Hot data lives on fast media like memory or SSD and serves frequent low latency reads.
- Warm data moves to cheaper disk where access is slower but still online.
- Cold data lands in archival storage like object storage with retrieval delays measured in minutes or hours.
Moving Between Tiers
A lifecycle policy demotes data as it ages or as access drops, and may promote it back if it gets hot again. The savings are large because cold tiers can cost an order of magnitude less per byte. The risk is a wrong guess: data demoted to cold that is suddenly needed pays a steep retrieval penalty.
Key idea
Tiered storage demotes aging or rarely accessed data from hot to warm to cold media, cutting cost per byte while risking slow retrieval if cold data is suddenly needed.