Multithreaded Read & Write Patterns
The multithreaded tests simulate a situation when there are one to four clients accessing the hard disk at the same time – the clients’ address zones do not overlap. We will discuss diagrams for a request queue of 1 as the most illustrative ones. When the queue is 2 or more requests long, the speed doesn’t depend much on the number of simultaneously running applications. You can also click the following links for the full results:
- IOMeter: Multithreaded Read, part 1
- IOMeter: Multithreaded Read, part 2
- IOMeter: Multithreaded Write, part 1
- IOMeter: Multithreaded Write, part 2
According to our new testing method, the distance between the data threads has become longer, so the HDD has to move its heads more to switch from one thread to another. What’s the outcome? Most of the Western Digital drives and the Samsung EcoGreen F2 slump down as soon as there appears a second thread to read. Two HDDs maintain an acceptable speed, though. These are the new Caviar Green MVW and the audio/video-optimized AV-GP. We could expect the latter to have advanced look-ahead reading algorithms, but it is unclear why the new 2-terabyte Green drive is so fast here. We even looked at the detailed results and made sure that it was indeed reading both data threads at about the same speed irrespective of the request queue depth.
Excepting the EcoGreen F2, the Samsung drives all slow down by half. The Hitachi drives do the same, the new firmware being somewhat worse than the older one.
We’ve got interesting results when the number of data threads is increased further. The Hitachi drives join the leaders, delivering a combined read speed of 100 MBps. This time, the new firmware looks better than the old one. Samsung’s HDDs split up into two groups: the F4 series are more than two times as fast as their F3 series mates.
Except for the above-mentioned two models, the Western Digital drives do not recognize the load and deliver low performance. Their heads are just reading all the threads one by one without using any look-ahead reading algorithms, and this turns to be a very slow strategy.
Multithreaded writing is simpler and we don’t see the HDDs differ as much as at multithreaded reading. We’ve got a group of leaders including the Samsung EcoGreen F4EG and WD’s 1.5-terabyte Caviar Black and RE4. We also have a group of losers including the Hitachi drives, the Samsung EcoGreen F2 and the WD AV-GP. A large cache and a lot of big and dense platters are the crucial factors for this test.