The design and use of persistent memory on the DNCP hardware fault-tolerant platform

Systems that are designed to recover from system failure due to software faults of the operating system and/or application typically require a means of persistently storing a subset of the state of the application. Disk drives are most often used as this persistent storage, but at a performance cost incurred repeatedly during normal execution as well as again at recovery time. Academic work has pioneered the concept of using a region of conventional memory, protecting it, and making it persist across operating system crashes and reboots, and making it as reliable as a disk. This can be used in place of a disk to alleviate the performance penalties noted above. This paper describes a project to take these concepts and apply them in a RAM disk-based realization of persistent memory (PM) as part of the Lucent DNCP (Distributed Network Control Platform) hardware fault-tolerant platform and implemented for the HP-UX operating system, focusing on its use by a main-memory database (MMDB) system. While we found that the reduction in recovery time was small relative to the reboot time, we achieved a nearly 40% reduction in execution time for an MMDB benchmark run on the PM as opposed to its normal use of a disk for achieving recoverability.