Blocks are the fundamental units of data storage at the NDB layer. Blocks are always assigned in sizes that are multiples of 64 bytes and are always aligned on 64-byte boundaries. The maximum size of any block is 8 kilobytes (8192 bytes).
Similar to pages, each block stores its metadata in a block trailer placed at the very end of the block so that the end of the trailer is aligned with the end of the block.
Blocks generally fall into one of two categories: data blocks and subnode blocks. Data blocks are used to store raw data, where subnode blocks are used to represent nodes contained within a node.
The storage capacity of each data block is the size of the data block (from 64 to 8192 bytes) minus the size of the trailer block.