WOW: wise ordering for writes - combining spatial and temporal locality in non-volatile caches
Binny S. Gill, Dharmendra S. Modha · 2005
Abstract — Write caches using fast, non-volatile storage are now widely used in modern storage controllers since they enable hiding latency on writes. Effective algorithms for write cache management are extremely important since (i) in RAID-5, due to read-modify-write and parity updates, each write may cause up to four separate disk seeks while a read miss causes only a single disk seek; and (ii) typically, write cache size is much smaller than the read cache size – a proportion of 1:16 is typical. A write caching policy must decide: what data to destage. On one hand, to exploit temporal locality, we would like to destage data that is least likely to be re-written soon with the goal of minimizing the total number of destages. This is normally achieved using a caching algorithm such as LRW (least recently written). However, a read cache has a very