The next test measures the average access speed. The minimum addressable data block, i.e. one sector, is used. IOMeter is bombarding the HDD for 10 minutes with requests to read and write random-address sectors at a request queue depth of 1.
The results are surprising. The HDDs from Seagate have the best access time at reading but one of them, the Barracuda 7200.11, is just awful when doing writing!
We saw this before with Seagate’s drives when we reviewed the NL35 and Barracuda 7200.9 in our Seagate Barracuda 7200.10 review. We learned then that it was due to the HDDs doing write verification. The point of this feature is that the HDD reads the data it has just written to verify their integrity.
Seagate began to tout this feature in the Barracuda ES model and then we learned when it was enabled. According to the Seagate documentation, the write verification is enabled for Barracuda ES drives when the HDD is functioning under uncomfortable temperature conditions, when it is either too cool (below 18°C) or too hot (over 58°C).
In Russia, hot-headed revolutionaries used to be sent to Siberia to cool down a little. And we sent our Seagate drive into a thermal chamber. Setting the chamber temperature at -5°C we managed to cool the HDD to 17°C. To reach the top threshold of the write verification mechanism we set the chamber at 45°C. In both cases we could spot the verification feature getting enabled by means of Getsmart and an IOMeter pattern that was sending requests to write random-address sectors.
So, this is what we had with the Barracuda ES but not only with it. Some OEM drives from Seagate, from server and desktop series alike, verified their writing under any temperature conditions (perhaps Seagate’s OEM partners demanded more reliability).
On my part, I can claim that the HDD was under comfortable conditions (25-30°C) during my tests. The Barracuda 7200.11 can’t blame me for cruel treatment!
I can also note the good results of the Hitachi drives. They are somewhat inferior to the Seagate team at reading, but are the best at writing.
The HDD from Western Digital is the slowest in this test because its platters, as I’ve shown you above, rotate at only 5400rpm. Interestingly, if you subtract 1.36 milliseconds from the read access time of the Western Digital drive (it is the difference between the half-rotation of a 7200rpm and a 5400rpm drive), you get the read access time of the Samsung.
In the beginning of this review I mentioned possible performance benefits HDDs with more platters and heads can get. It’s time to check this out in practice.
The average access time is not the only factor comparing HDDs with different recording density (because the HDD doesn’t move its heads around the entire platter in real applications), so we have decided to introduce a new parameter that would count in the head movement speed and depend on the number of platters and on the platter density. We call it the Average Positioning Speed.
This parameter is easy to calculate: the HDD is being requested to read random-address sectors for a while but instead of averaging the time it takes to perform all the requests we average the difference between the LBA addresses of the previous and next read sector divided by the time it takes to perform this disk operation. As a result, we have the average amount of data the heads go through in each second.
Here are the results:
Hitachi’s HDDs were inferior to the Seagate in the standard test of average access time, but are faster in terms of Average Positioning Speed. We did not introduce the new parameter with the purpose of making Hitachi the winner, yet it is a noteworthy thing. Combining a good seek time with a large number of read/write heads, the Hitachi drives should benefit from short seeks – and they do!