Articles: Storage

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Response Time

Besides the firmware algorithms, the results of the Database test are affected by the disk access time. Let’s see how it differs between the HDDs. In this test IOMeter is sending a stream of requests to read and write 512-byte data blocks with a request queue of 1 for 10 minutes. The total number of requests processed by the HDD is over 60 thousand, so we get a sustained response time that doesn’t depend on the HDD’s buffer size. The results are sorted by read response time.

The Seagate is the best one at reading, enjoying a 1.21ms lead over the closest pursuer. That’s quite a difference. It is followed by three drives with similar results, namely the HDDs from Western Digital, Samsung (this partially explains the performance of this HDD in the previous test), and Fujitsu.

It’s all very different at writing: the Seagate turns a loser while the Toshiba and Western Digital go ahead.

It’s interesting to compare the ratio of response times at writing and reading which indicates how aggressive the HDD’s deferred writing algorithms are. The smaller the ratio, the more requests the HDD can store in its memory. This ratio is within 0.47 to 0.54 for every HDD except the Seagate whereas the ST9160821AS has a write/read response ratio of 0.65. This parameter equals 0.50 for the HM160JI which doesn’t quite agree with its Database diagram. This must be due to some peculiarity of this HDD’s firmware algorithms (the Database pattern operates with 8KB data blocks).

Random Read & Write Patterns

The HDD is being bombarded with requests to read and write random-address data blocks of varying size.

There’s nothing interesting at reading: the drives all have the same shape of the graph while the places are distributed according to the read response time they have shown in the previous test. The Seagate enjoys a large lead while the others go in a dense group.

It’s more interesting at writing. The HDDs perform differently now and take places according to the results they had in the write response test. Note the results of the Samsung – it slows down suddenly with small data blocks, becoming slower than the ST9160821AS on 512-byte blocks. By the way, it is not the Seagate, but the Hitachi that is the slowest drive with large data blocks.

And now we can proceed from synthetic to more real-life tests.

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