file storage, block size and input splits in Hadoop

1 block will hold all these files. It has some extra space. If new files are added, it will accommodate here [...] is it one because all the 4 files are contained with in a block?

You'll actually have 4 blocks. It doesn't matter if all files can fit into a single block or not.

EDIT:Blocks belong to a file, not the other way around. HDFS is designed to store large files that are almost certainly going to be larger than your block size. Storing multiple files per block would add unnecessary complexity to the namenode...

• Instead of a file being blk0001, it's now blk0001 {file-start -> file-end}.
• How do you append to a file?
• What happens when you delete a file?
• Etc...

or is it one input split per file?

Still 1 split per file.

how is this determined?

This is how.

what if I want all files to be processed as a single input split?

Use a different input format, such as MultipleFileInputFormat.

1. Each file will get stored in a separate block but file does not occupy a full block of underlying storage, it would use less physical storage.

2. HDFS is not for smaller files - check this out