HDFS NameNode Heap Estimation

Hadoop Distributed File System (HDFS) is a distributed file system designed for high-performance data access in Hadoop clusters, featuring a NameNode (Master) and DataNode (Worker) architecture. HDFS ensures high availability and data durability by distributing data across servers and replicating it.

Estimating NameNode Heap Memory

The estimation of NameNode's heap memory in Acceldata ODP clusters can be approached in two primary methods: considering the number of file inodes and blocks, or by evaluating the cluster capacity.

Example: Estimating Cluster Capacity

Let's illustrate with an example of calculating cluster capacity:

Assume the number of DataNodes in a cluster is 200.

Each DataNode's HDFS storage allocation is 24TB (with 2TB allocated for HDFS DataNode mounts per 12 disks).

Cluster Capacity = (Individual DataNode's HDFS Storage Size) * (Total Number of DataNodes in Cluster)

Example Calculation:

Cluster Capacity = 200 * 24 = 4800TB

Calculating NameNode's Heap Memory Requirement

Using the above cluster size, the required heap memory for the NameNode can be determined. It is essential to consider the Block Size and Replication Factor, as they influence the number of blocks in a cluster.

Let's assume the default HDFS Block Size is 128MB.

Disk space required for a block = (Block Size) * (Replication Factor)

For a replication factor of 1:

Disk Space for a Block = 128 * 1 = 128MB

Total blocks that can be stored in the cluster:

Total Blocks = [Cluster Capacity (in MBs)] / (Disk Space for a Block)

Thus, 4,800,000,000 MB (4800TB) / 128 = 36,000,000 blocks

As a rule of thumb, for every 1 million blocks, approximately 1GB of Heap memory is required for the NameNode. Therefore, for 36 million blocks, approximately 36GB of NameNode heap memory is recommended.

If the Replication Factor is increased to 3, the block size would be 384MB per block.

Total Blocks in Cluster = 4,800,000,000 MB (4800TB) / 384 = 12,000,000 blocks

According to recommendations, for these 12 million blocks, approximately 12GB of Heap memory is required for the NameNode.

Monitoring NameNode's Heap Memory from Pulse

NameNode's heap memory allocation and usage can be monitored using Acceldata Pulse Dashboards: https://docs.acceldata.io/pulse/documentation/hdfs-dashboard