Random Read & Write Patterns

Now we’ll see the dependence between the drives’ performance in random read and write modes on the size of the data block size.

We will discuss the results of the disk subsystems at processing random-address data in two versions. For small-size data chunks we will draw graphs showing the dependence of the amount of operations per second on the data chunk size. For large chunks we will compare performance depending on data-transfer rate in megabytes per second. This approach helps us evaluate the disk subsystem’s performance in two typical scenarios: working with small data chunks is typical for databases. The amount of operations per second is more important than sheer speed then. Working with large data blocks is nearly the same as working with small files, and the traditional measurement of speed in megabytes per second becomes more relevant.

IOMeter: Random Read, operations per second

Random reading in small blocks is where flash memory knows no rival unless you count in such specific devices as RAM-based drives. Even early SSDs were incomparable to HDDs in this test. The ten-channel controller employed in the X25-M improves performance even more. For example, the X25-M delivers almost 6,000 operations per second on 8KB data chunks (not the smallest, but frequently used size of a data block) whereas the best of HDDs only deliver 200 operations per second. As you can guess, even a multi-disk RAID cannot match the SSDs here.

IOMeter: Random Read, MBps

The difference isn’t big on large data blocks but the X25-M is still in the lead. Samsung’s SSD is slower than the HDDs after a certain size of the data chunk due to its low sequential speed.

IOMeter: Random Write, operations per second

The dramatic reduction of response time at writing helps the X25-M win the test of random writing in small blocks whereas Samsung’s SSD is far slower than its opponents (it was slower even than 2.5-inch HDDs in our previous test session). The twofold advantage over the 15,000rpm HDD in terms of random-address write operations is a superb result. Take note of the sudden performance jump on 2KB data blocks. Our test program doesn’t include 4KB data blocks, so we’ve got a question we will try to answer in our next review: if the drive’s performance goes down on 512-byte data blocks or there is a sudden increase in performance on data chunks of 4KB or similar size? Anyway, this is a superb result for a MLC-based flash drive.

IOMeter: Random Write, MBps

It is the speed of sequential writing that affects the results on large data blocks. Samsung’s SSD improves somewhat as the data chunks grows larger (its write access time was even more of a problem than its low sequential write speed) while the X25-M maintains the same speed throughout the test. Although the latter is somewhat slower than modern HDDs on very large data blocks, the gap isn’t large. The ten-channel controller helps this SSD again.