Western Digital 20,000 RPM HDD

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It still won't compete in random I/O.

HDDs now do like 80-150 (true) random read IOps - SSDs go towards 100.000 or even a million (enterprise products). The Intel SSD is between 50.000 and 80.000 depending on what review you trust. But as you see - you won't fix this with a little more rpm.

Maths is surprisingly not my best subject, but i guess you could calculate how many rpm a HDD has to be in order to compete with SSDs on random I/O. I guess this would be a very large number. :)
 

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I tried comparing read access times using Toms storage charts:

14.5ms 5400rpm WD Green 1TB
11.9ms 7200rpm WD RE4 2TB
7.1ms 10.000rpm Velociraptor 300GB
5.5ms 15.000rpm Atlas 15K II
..
..
0.1ms SSD

Even lower than 0.1ms actually, and it can process multiple I/O's at once which HDDs cannot do. Intel SSDs for example use the NCQ feature meant to shorten HDD access times on multi-queue I/O - is now being used to provide command queueing (buffering) so the SSD actually gets enough 'work' to perform like it should - while otherwise the SSD would not get enough I/O requests to saturate its 8 parallel flash channels.

HDDs are dying; they will soon not be used anymore for the system drive - banished to storing large bulky files only - until SSDs are matured to a point all storage will become electrical/solid state.
 

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