Fast boot
摘要
說(shuō)明書(shū)
In some embodiments, the NAM is notified, using the cache coherency protocol, of any transition from primary or exclusive to secondary (i.e., the NAM is copied on those transitions). Thus, the NAM is updated any time a page transitions from being exclusive or prime to secondary. If a page p on a node N becomes secondary, then the page on the NAM must also be updated to become a secondary. Thus, the NAM preserves the state of a set of pages that it believes are valid, and, in some embodiments, the NAM has the “ultimate” reference copy (or an approximation) of the official memory of the TidalPod.
In some embodiments, if it is detected that the TidalPod is failing or coming down, then the NAM makes read requests for copies of all primary pages in the TidalPod, which the NAM does not already have, which will be marked as secondary on the NAM. Given sufficient time, this will result in the NAM having all secondary copies of the pages on the nodes in the TidalPod (and becoming, for example, an “ultimate reference copy”). As one example, suppose that a failure or error is detected. The NAM searches through all of its pages to determine which pages are invalid. The NAM attempts to make them valid by making a read request for copies of those pages from other nodes in the TidalPod. If copies are obtained from other nodes, then the NAM updates its invalid page with the obtained copy of the page, which is then made valid and secondary on the NAM.
In some embodiments, the NAM includes backup systems, such as batteries on the motherboard that allow the NAM to continue to function, for example, during a system shutdown or loss of power. This provides the NAM with time to request secondary copies of pages on other nodes in the TidalPod (to transition from an invalid page to a valid secondary). This allows the NAM to complete itself in a failure situation.
