Quick 'n' dirty write performance test

SimpleIoTest.java

import java.io.*;
import java.util.*;
import java.security.SecureRandom;

public class SimpleIoTest {
	private static final int BLOCK_SIZE = 1024 * 1024;
	private static final int TOTAL_SIZE = 1024 * 1024 * 1024;
	private static final int SEQUENTIAL_ITERATIONS = 32;
	private static final int RANDOM_ITERATIONS = 16;

	private static final byte[] CRUMMY_RANDOM = new byte[TOTAL_SIZE];

	public static void main(String[] args) throws Exception {
		System.out.print("Generating random data... ");
		System.out.flush();

		new Random().nextBytes(CRUMMY_RANDOM);
		int indexCount = CRUMMY_RANDOM.length / BLOCK_SIZE;
		int[] indexes = SecureRandom.getInstance("SHA1PRNG").ints(0, indexCount).limit(indexCount).map(i -> BLOCK_SIZE * i).toArray();

		System.out.println("done");
		System.out.flush();

		File dest = File.createTempFile("iotest-", ".tmp", new File("."));
		dest.deleteOnExit();
		RandomAccessFile file = new RandomAccessFile(dest, "rwd");

		System.out.print("Performing sequential write... ");
		System.out.flush();

		long startNanos = System.nanoTime();
		for (int i = 0; i < SEQUENTIAL_ITERATIONS; i++) {
			file.write(CRUMMY_RANDOM);
			file.seek(0);
		}
		long endNanos = System.nanoTime();

		System.out.printf("%,.0f bytes/sec\n", (SEQUENTIAL_ITERATIONS * (double) CRUMMY_RANDOM.length) / ((endNanos - startNanos) / 1_000_000_000d));
		System.out.flush();

		System.out.print("Performing random-access write... ");
		System.out.flush();

		startNanos = System.nanoTime();
		for (int iter = 0; iter < RANDOM_ITERATIONS; iter++) {
			for (int i = 0; i < indexes.length; i++) {
				int index = indexes[i];
				file.seek(index);
				file.write(CRUMMY_RANDOM, index, BLOCK_SIZE);
			}
		}
		endNanos = System.nanoTime();

		System.out.printf("%,.0f bytes/sec\n", (RANDOM_ITERATIONS * (double) CRUMMY_RANDOM.length) / ((endNanos - startNanos) / 1_000_000_000d));
		System.out.flush();
	}
}

This was thrown together quickly, so there may be bugs. Note that it only attempts to benchmark write performance, as read performance is more difficult due to caching.

Adjust SEQUENTIAL_ITERATIONS and RANDOM_ITERATIONS as desired.

Suggested usage:

javac SimpleIoTest.java
sudo ionice -c 1 `which java` SimpleIoTest