Multi-Threaded Read & Write Patterns

The multi-threaded tests simulate a situation when there are one to four clients accessing the hard disk at the same time. The depth of the outgoing request queue is varied from 1 to 8, and the address zones of the applications (called Workers in IOMeter) do not overlap.

You can follow the links below to see tables with results, but we’ll discuss diagrams for a request queue of 1 as the most illustrative ones. When the queue is longer, the speeds depend but little on the number of applications.

• IOMeter: Multi-threaded Read results
• IOMeter: Multi-threaded Write results

Multithreaded reading is a very difficult operation for HDDs because they have to move their read/write heads among multiple streams located in different parts of the platters, but for an SSD this load is hardly different from ordinary sequential reading. An SSD doesn’t care about the order of reading. As a result, the X25-M does not slow down but even accelerates in this test, winning it due to its high sequential speed.

It’s different with multithreaded writing. The drives can now collect data in their cache and write in large blocks. Writing is more difficult for an SSD than reading, and it has a lower speed of sequential writing even though it doesn’t have to move anything among the test zones. Thus, an SSD’s speed of multithreaded writing is similar to its sequential write speed. The latter is quite high with the X25-M, so it is not far slower than the HDDs in this test.