|| at Nov 16, 2009 at 10:22 pm
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
On 11/16/09 12:45 PM, "Steve Gao" 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.