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Memory-to-data ratio

As explained in ScyllaDB in Action

The RAM-to-disk storage ratio is the amount of system memory relative to the persistent disk capacity available to a database.

The memory-to-disk storage ratio compares a database’s RAM with its available persistent disk capacity. In ScyllaDB, RAM supports an in-memory cache; too little cache sends more reads to disk and slows them. section 9.2.2

Use these ratios as practical starting points:

  • Stay above 1:100: provide at least 1 GB of RAM for every 100 GB of disk. section 9.2.2
  • Target 1:30 when practical: provide about 1 GB of RAM for every 30 GB of disk, while recognizing that workloads vary. section 9.2.2

Sizing a node

A node with 100 GB of disk should have at least 1 GB of RAM to remain above the suggested threshold. A 1:30 target would pair that capacity with roughly 3.3 GB of RAM. section 9.2.2

How ScyllaDB in Action covers it

How deep it goes
Defines threshold and optimal ratios, explains cache consequences, and stops short of workload-specific sizing.
Examples
Uses 1 GB of RAM per 100 GB of disk and a preferred 1:30 comparison.
What it assumes
Assumes basic awareness of RAM, persistent storage, and database reads.
What you can do after
Evaluate node memory requirements against disk capacity and anticipate read-performance consequences.
How it connects
Connects memory sizing to in-memory cache, disk reads, compactions, repairs, and gossip.
Cover of ScyllaDB in Action
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