Operating Systems: Concurrent and Distributed Software Design

15.7. Non-volatile memory

Non-volatile RAM (NVRAM) costs about four times as much as normal RAM and has become available in increasingly large units, currently up to about 10 megabytes. A cheaper alternative is battery-backed RAM. There are many potential uses for non-volatile memory, for example:

• for caching data in a file storage service. This allows fast response to write requests, but gives the assurance that the data is stored securely, normally achieved by an acknowledged write out to disk;

• to hold the file service's data structures. When a change is made it need not be written out immediately, to achieve consistency of the stored filing system;

• to accumulate requests for writes to disk and to order them for use by an efficient disk-arm scheduling ...