NameNode metadata - is in memory data structures describing file system structure (directories, files, and file's blocks).
NameNode image is on-disk representation of the metadata. (fsimage file). Edit logs - is a journal that keeps all the events that cause changes in the metadata and allows restoration in case of NameNode failure. Secondary Namenode - runs checkpoints from time to time. During a checkpoint edit logs are merged into metadata and saved to fsimage, which is pushed to the NameNode. Boris. On 11/16/09 12:45 PM, "Steve Gao" <steve....@yahoo.com> wrote: > What are the differences between the 3 concepts: (1) namenode metadata, (2) > namenode image, and (3) edit logs? > > BTW,I know the secondary namenode backups namenode data. > > I was told that there is another daemon which also backups meta data . Is that > true? What is the daemon? Thanks. > > > > > >
