CODEWITHSUNDEEP
javalinuxperformanceio
rickfeng
rickfeng

Reputation: 21

about linux IO performance

I wrote a program to test IO performance in java useing FileChannel. Write data and call force(false) immediately. My Linux server has 12 ssd hard drives, sda~sdl, and I test writing data to different hard drive, the performance varies widely, and I don't know why?

code:

public static void main(String[] args) throws IOException, InterruptedException {
    RandomAccessFile aFile = new RandomAccessFile(args[0], "rw");
    int count = Integer.parseInt(args[1]);
    int idx = count;
    FileChannel channel = aFile.getChannel();
    long time = 0;
    long bytes = 0;
    while (--idx > 0) {
        String newData = "New String to write to file..." + System.currentTimeMillis();
        String buff = "";
        for (int i = 0 ; i<100; i++) {
            buff += newData;
        }
        bytes += buff.length();
        ByteBuffer buf = ByteBuffer.allocate(buff.length());
        buf.clear();
        buf.put(buff.getBytes());
        buf.flip();
        while(buf.hasRemaining()) {
            channel.write(buf);
        }
        long st = System.nanoTime();
        channel.force(false);
        long et = System.nanoTime();
        System.out.println("force time : " + (et - st));
        time += (et -st);
    }
    System.out.println("wirte " + count + " record, " + bytes + " bytes, force avg time : " + time/count);
}

Result like this:
sda: wirte 1000000 record, 4299995700 bytes, force avg time : 273480 ns
sdb: wirte 100000 record, 429995700 bytes, force avg time : 5868387 ns

The average time vary significantly.

Here is some IO monitor data.
sda: iostat data image
sdb: iostat data image

Upvotes: 1

Views: 108

Answers (1)

Tim Connor
Tim Connor

Reputation: 97

You need to start by measure your SSD disks performance using some standard tool like fio.

Then you can test your utility again using numbers from fio output.

Looks like you are writing into the Linux write cache so that can explain your results :)

Upvotes: 1

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