Introduction. HDFS rolling upgrade allows upgrading individual HDFS daemons. For examples, the datanodes can be upgraded independent of the namenodes. A namenode can be upgraded independent of the other namenodes. The namenodes can be upgraded independent of datanodes and journal nodes.
How can you prevent the cluster from downtime during updates to the NameNode system?
To prevent the HA cluster from a split-brain scenario, the administrator must configure at least one fencing method. It ensures that only one NameNode is active at a time. The fencing method can include the killing of the NameNode process and preventing its access to the shared storage directory.
How does Hadoop increase cluster size?
The most common practice to size a Hadoop cluster is sizing the cluster based on the amount of storage required. The more data into the system, the more will be the machines required. Each time you add a new node to the cluster, you get more computing resources in addition to the new storage capacity.
How many Namenodes can be there in a cluster?
You can have only a single name node in a cluster. Detail – In Yarn / Hadoop 2.0 they have come with a concept of active name node and standby name node. ( This is where most of the people get confused. They consider them to be 2 nodes in a cluster).
What does NameNode format do?
When we format namenode(bin/hadoop namenode -format) it formats the meta-data related to data-nodes. By doing that, all the information on the datanodes are lost and the datanodes becomes reusable for new data.
What is HDFS NameNode?
The NameNode is the centerpiece of an HDFS file system. It keeps the directory tree of all files in the file system, and tracks where across the cluster the file data is kept. The NameNode responds the successful requests by returning a list of relevant DataNode servers where the data lives.
How do I know if NameNode is active?
- List the namenode hostnames. # hdfs getconf -namenodes. c2301-node2.coelab.cloudera.com c2301-node3.coelab.cloudera.com.
- Get nameservice name. # hdfs getconf -confKey dfs.nameservices. nameservice1.
- Get active and standby namenodes. # hdfs getconf -confKey dfs.ha.namenodes.nameservice1. namenode11,namenode20. # su – hdfs.
When NameNode fails which node takes the responsibility of active node?
When active node fails, then Passive node takes the responsibility of active node. Passive node is also called standby namenode that takes the responsibility to remove the problem of single point of failure (SPOF).
How will you decide the size of your Hadoop cluster?
1 Answer
- Bare minimum, depending on replication factor of 3, you need about 50TB (10×3=30TB 80% rule: 40TB usable, this give you 8TB to work with ) – So 5 Nodes at 10TB a piece for HDFS.
- HDFS can only use a maximum of 80% of total cluster space.
- More nodes = faster YARN jobs.
Why are there 3 nodes in Hadoop?
NameNode is the centerpiece of HDFS. NameNode only stores the metadata of HDFS – the directory tree of all files in the file system, and tracks the files across the cluster. 3. NameNode does not store the actual data or the dataset.
How many NameNodes are in a Hadoop cluster?
Hadoop 2.2 has two Namenodes- Active Namenode and Passive Namenode.
What is a rolling upgrade in HDFS?
HDFS rolling upgrade allows upgrading individual HDFS daemons. For examples, the datanodes can be upgraded independent of the namenodes. A namenode can be upgraded independent of the other namenodes. The namenodes can be upgraded independent of datanodes and journal nodes.
Can I upgrade Hadoop HDFS without incurring downtime?
In Hadoop v2, HDFS supports highly-available (HA) namenode services and wire compatibility. These two capabilities make it feasible to upgrade HDFS without incurring HDFS downtime.
How do I finalize my HDFS cluster?
You can check with the following command whether the cluster needs to be finalized: Run the actual finalize command to make the HDFS upgrade permanent: The -finalizeUpgrade command removes the previous version of the NameNode’s and DataNodes’ storage directories.
How do I rollback a DFS upgrade?
Prepare Rolling Upgrade Run “ hdfs dfsadmin -rollingUpgrade prepare ” to create a fsimage for rollback. Run “ hdfs dfsadmin -rollingUpgrade query ” to check the status of the rollback image. Wait and re-run the command until the “ Proceed with rolling upgrade ” message is shown.
