Database Reference
In-Depth Information
The Quorum-based storage
In the Quorum-based storage HA technique, the two namenodes use a
Quorum Journal
Manager
(
QJM
) to share edit logs. As we already know, edits log is the activity log of all
file operations on the cluster. Both the active namenode and the standby namenode need to
have their edit logs file in sync. To achieve this, the active namenode communicates with
the standby namenode using the
JournalNode
(
JN
) daemons. The active namenode reports
every change of its edits logs file to the JournalNodes daemons. The standby namenode
reads the edit logs from the JournalNodes daemons and applies all changes to its own
namespace. By doing this, the two namenodes are always in sync.
In the following diagram, you see a typical architecture of HDFS HA using QJM. There are
two namenodes, active and standby, that communicate with each other via JournalNodes.
