Home > Storage > PowerScale (Isilon) > Product Documentation > Storage (general) > PowerScale OneFS Best Practices > OneFS caching recommendations
OneFS uses up to three levels of read cache, plus an NVRAM-backed write cache, or coalescer, as shown in the following figure.
The first two types of read cache, level 1 (L1) and level 2 (L2), are memory (RAM) based, and analogous to the cache used in processors (CPUs). These two cache layers are present in all storage nodes.
An optional third tier of read cache, called SmartFlash or Level 3 cache (L3), is also configurable on nodes that contain solid state drives (SSDs). SmartFlash (L3 cache) is an eviction cache that is populated by L2 cache blocks as they are aged out from memory.