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Mongoose is a high-load storage performance testing tool
There is a newer version: 4.3.10
package com.emc.mongoose.base.data;

import static java.nio.file.StandardOpenOption.READ;

import com.github.akurilov.commons.math.MathUtil;
import com.github.akurilov.commons.system.SizeInBytes;
import java.io.Closeable;
import java.io.File;
import java.io.IOException;
import java.nio.ByteBuffer;
import java.nio.MappedByteBuffer;
import java.nio.channels.ReadableByteChannel;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;

/** Created by kurila on 29.09.14. A finite data input for data generation purposes. */
public interface DataInput extends Closeable {

	enum Type {
		FILE, SEED
	}

	int getSize();

	MappedByteBuffer getLayer(final int layerIndex);

	static DataInput instance(
					final String inputFilePath,
					final String seed,
					final SizeInBytes layerSize,
					final int layerCacheLimit)
					throws IOException, IllegalStateException, IllegalArgumentException {
		final DataInput instance;
		final long layerSizeBytes = layerSize.get();
		if (layerSizeBytes > Integer.MAX_VALUE) {
			throw new IllegalArgumentException("Item data layer size should be less than 2GB");
		}
		if (inputFilePath != null && !inputFilePath.isEmpty()) {
			final Path p = Paths.get(inputFilePath);
			if (Files.exists(p) && !Files.isDirectory(p) && Files.isReadable(p)) {
				final File f = p.toFile();
				final long fileSize = f.length();
				if (fileSize > 0) {
					if (fileSize > Integer.MAX_VALUE) {
						throw new AssertionError("Item data input file size should be less than 2GB");
					}
					try (final ReadableByteChannel rbc = Files.newByteChannel(p, READ)) {
						instance = new ExternalDataInput(rbc, (int) layerSizeBytes, layerCacheLimit);
					}
				} else {
					throw new AssertionError("Item data input file @" + p.toAbsolutePath() + " is empty");
				}
			} else {
				throw new AssertionError(
								"Item data input file @"
												+ p.toAbsolutePath()
												+ " doesn't exist/not readable/is a directory");
			}
		} else {
			instance = new SeedDataInput(Long.parseLong(seed, 0x10), (int) layerSizeBytes, layerCacheLimit);
		}
		return instance;
	}

	static void generateData(final MappedByteBuffer byteLayer, final long seed) {
		final int ringBuffSize = byteLayer.capacity();
		final int countWordBytes = Long.SIZE / Byte.SIZE;
		final int countWords = ringBuffSize / countWordBytes;
		final int countTailBytes = ringBuffSize % countWordBytes;
		long word = seed;
		int i;
		// 64-bit words
		byteLayer.clear();
		for (i = 0; i < countWords; i++) {
			byteLayer.putLong(word);
			word = MathUtil.xorShift(word);
		}
		// tail bytes
		final ByteBuffer tailBytes = ByteBuffer.allocate(countWordBytes);
		tailBytes.asLongBuffer().put(word).rewind();
		for (i = 0; i < countTailBytes; i++) {
			byteLayer.put(countWordBytes * countWords + i, tailBytes.get(i));
		}
	}
}