Home > Storage > PowerScale (Isilon) > Product Documentation > Storage (general) > PowerScale OneFS SmartFlash > In-line compression and caching
To support OneFS inline compression, a node’s L1, or client-side, read cache is divided into separate address spaces. That way, both the on-disk compressed data and the logical uncompressed data can be cached. The address space for the L1 cache is already split for data and FEC blocks, so a similar technique is used to divide it again. Data in the uncompressed L1 cache is fed from data in the compressed L1 cache which, in turn, is fed from disk.
OneFS prefetch caching has also been enhanced to accommodate compressed data. Because reading part of a compressed chunk results in the entire compression chunk being cached, it means that prefetch requests are rounded to compression chunk boundaries. Because a prefetch request is not complete until the uncompressed data is available in cache, the callback used for prefetch requests performs the decompression.