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I am looking at buying a new HD for a homegrown server and see that one of the candidates has a SATA interface with "3.0 GB/s" but it has a disk speed of 7200 RPMs.

Obviously, the SATA speed is a measure of how much throughput the SATA controller can handle, whereas the disk speed refers to how fast the disks can spin.

My questions are:

  • When it comes to how fast a machine can R/W data to disk, which of these speeds is more critical?
  • What types of applications are better suited for a disk with a faster SATA interface? What types of applications are better suited for a disk with more RPMs?

I'm basically looking for a way to say "Hey, on this server I'm going to run x, y and z applications, and given the choice of faster SATA throughput or faster RPMs, I'll choose w."

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storagereview.com for benchmarks. The speed limits of the SATA interfaces are more or less never hit; they are theoretical max limits for the bus. Look at throughtput and seek time for different drives; figures on random accesses and continuous reads and writes. Depending on application, weigh these numbers differently. –  Daniel Andersson May 17 '12 at 15:21
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"The speed ... of the SATA ... are ... never hit" - Repetition of a widespread misconception. The SATA transfer rate is the speed of the bits on the wire; there is no variable bit-speed on SATA. People confuse actual transfer rate plus idle time on the bus with the averaged transfer rates (over a time interval). Of course the average rate is never as high as the actual rate! SATA transfers are ATAPI command requests and responses as well as sector data. A faster link between the device (e.g. HDD) and host (the PC) is always beneficial. –  sawdust May 17 '12 at 20:24
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1 Answer

up vote 1 down vote accepted

When it comes to short quick bursts of data , the interface and cache sizes come into play, both the system caches and the disks own caches.

When it comes to data that doesnt fit in any of that stuff (aka 99% of everything :-) the platter speeds are the big bottlenecks , where the speed of the continual transfer of data is important.

I would have to say that everything advantages, the faster you get it on the platter, the sooner it is in reality finished, anything else is it still moving about in some aspects of the hardware. I/O is I/O, and can effect I/O in the rest of the computer. This becomes more important, when there is more than ONE thing going on.
The connection speed, is just as important to get it in and out and around quick and be done with that.

To the Platter is the matter:
If we are to specify things that are more effected by the disk platter speeds, and up to negativly effected by the stupid caching stuff, it is continual high data rate, Videos, large pictures, large databases accessed all at once , and when there is many other things going on filling and flushing these caches, simeltanious R/W I/O. If your really putting the computer to task, and doing lots of stuff at the same time, platter speed is everything.

Passing around in the rams and over fast connections
Things that fall into the cache size, and depending on the settings in the system, are most effected by the interface to the "ram" in the disks cache. so small quick I/O that is around 4-16megs. Regular sized picture, only the tiny videos, small docs, simple html, text, small files like parts of programs, dlls, plugs , and when there isnt 50 other things filling and clearing same said caches.
In these minimal uses of the computer, the caches are the speed, the rate you can get from/to those caches is everything. How long it takes to get to the platters, when there is not a lot of data, and nothing else going on, isnt really an issue.

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