# Hard Drive vs. SSD: How Read/Write Speeds are Measured ?



## Fren Banklin (Nov 6, 2008)

I'm looking at SSDs (Solid State Drives) for a possible new build. In reading reviews, etc... there are a lot of comparisons made between the Read/Write speeds of traditional Hard Drives, and the Read/Write speeds of SSD's, yet when I look up the specs of both types of drives on NewEgg, it seems as if the standard to measre the R/W speed of HD's is different than the standard to measure SSD's.

For SSD's, it's pretty straightforward. 200 MB/s (Megabytes per second), etc...

But HD's are measured in "Average Seek Time", "Average Write Time" and "Latency". What do these numbers mean, and how do they relate to basic throughput.

How can I (or anyone else considering purchasing an SSD) make an informed decision on the performance differences between traditional HD's and SSD's, if the standards to measure that performace are completely different from each other ?


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## raptor_pa (Dec 5, 2008)

It's kind of like 3GB/s SATA drives, never gonna see that much data flow down the wire with current technology, but it could.... Seek time is track to track seek, how long it takes to move across the surface. Write time is the time to package write and verify the write to a sector, latency is the rotational factor, after reading one sector passing under the head, what is the delay till the head is ready to read the next sector. This is pretty much used in the Logical sector mapping for the drive, where logical contiguous sectors are not the same as the physically contiguous sectors.


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## Fren Banklin (Nov 6, 2008)

raptor_pa said:


> It's kind of like 3GB/s SATA drives, never gonna see that much data flow down the wire with current technology, but it could.... Seek time is track to track seek, how long it takes to move across the surface. Write time is the time to package write and verify the write to a sector, latency is the rotational factor, after reading one sector passing under the head, what is the delay till the head is ready to read the next sector. This is pretty much used in the Logical sector mapping for the drive, where logical contiguous sectors are not the same as the physically contiguous sectors.



Okay then, for all of that; How do you compare the two ?


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## raptor_pa (Dec 5, 2008)

I don't know if there is a good comaprison from teh vendors. Best bet would be to look for third party comparisons of actual tested throughput on base configured systems. Like anything else, the manufacturer's numbers are average, like with Mileage numbers on vehicles.. your mileage may vary. But if you can find actual test results on comparable hardware, then the important numbers.. the difference in tested thruput would be available. No good answer tho how to do it from the manufacturer's tests. They always report the fastest they can...


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## Fren Banklin (Nov 6, 2008)

Er um. With all due respect, it sounds as if your answer is "there is none", and that simply is not acceptable, even if it's true.

I expect some expert to MAKE UP some numbers. I don't care about "mileage" and other metaphors, I want a number, a simple number. A standard 7500 rpm HD typical gets "X Mb/s", compared to 200 Mb/s for SSD's.

How are they going to sell these things, if they can't relate them to what their future customers already have ?

They have an objective standard to measure overall performance for GAMES. All these "round-ups" that have charts with numbers and stuff. If they can quantify all of that into a single number, they can compare SSD's to HD's.

Okay, enough whining.

Here's an idea, in case anyone is interested.

YouTube - SSD vs 7200rpm HD


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## raptor_pa (Dec 5, 2008)

I tend t agree, it is not the way it should be, and I don't know for sure if it is true that no true comparison exists. But like so many other things that are sold, it is all in the marketing. The manufacturers will only tell us the numbers that are in their favor, it will take true independent calibrated testing to get any information that is truly useful. And like anything else, it takes an organization with deep enough pockets to design, implement, validate and execute those tests.


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## BoT (Dec 16, 2008)

it's a new technology. although it does practically the same, it does so very differently.
SSD's have very low access times and very low latencies and they excel in read speeds, especially in random reads. 
it is not difficult for a mechanical hdd to outperform an ssd. this is a little bit more complicated but if you are really interested. here is a pretty decent read from anand.
take it with a grain of salt but i think it will give you a pretty good insite of what it is all about

Anandtech: The SSD Anthology

The SSD Update:


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## Fren Banklin (Nov 6, 2008)

I lost interest and started falling asleep here:



> Iometer is a tool that can simulate any combination of disk accesses you can think of. If you know how an application or OS hits the disk, iometer can simulate it. While random disk accesses are the reason that desktop/notebook hard drives feel so slow, the accesses are generally confined to particular areas of the disk. For example, when you’re writing a file the OS needs to update a table mapping the file you’re writing to the LBAs it allocated for the file. The table that contains all of the LBA mapping is most likely located far away from the file you’re writing, thus the process of writing files to the same area can look like random writes to two different groups of LBAs. But the accesses aren’t spread out across the entire drive.


One thing I like to do is come into a movie in the middle and try to figure out the past and the future both, while experiencing the present real-time.

The stakes are higher in both directions. You can either get rewarded or punished, you are right or you are wrong, in an increasing manner.

What is the equation used to describe the increase ?

Find out who say "There isn't one.", and compare the level of certainty/proveability they have with their answer to the level of certainty/proveability with the people that have other ideas. They say "It's possible..."

It could be "It's possible, but..." or it could be "It's possible, and..."

I like people that use "and" more often than they use "but". It's better I think to know what to include, than it is to know what to exclude. Both may be mathmatically equivalent in importance, however I think "and" people have a much-more positive dynamic. They are happier people, and people are happy to be around them.

Those that dedicate the entirety of their lives excluding thing have difficulty in maintaining the definition of the whole. Because once they have excluded everything that doesn't fit the definition, they have nothing to do be re-evaluate the definition that they used previously, and look for ways "to improve upon it" (and simultaneously give themselves something to do, other than continuously watch for difference.

"One of these things is not like the other."

You don't want that person to be you.

Guess the reading that I did manage to accomplish has apparantly rekindled an appreciation for day-dreaming, of pondering, or wondering, and other creative processes.

Sometimes when I read the text on this forum, certain letters transpose themselves right in front of me. I mean, one second I'm reading something and it means one thing, then something <shifts> and I'm reading something that means something completely different than it used to.

So I find the critical word, and read the sentence twice; once with the critical word transposed one way, and then again with it re-visualized another.

This mehotd seems to be effective in identifying the error. If you can imagine the incorrect text as correct (what you see versus what you tell yourself that you see), it should be no surprise that one can also see correct text as trasposed incorrectly, and accept that as if it were real.

Q: What happens when one comes to believe that there is a pattern to the errors ? If random doesn't exist, then there is no "random" quality to the errors; it's a pattern by defintion. What KIND of pattern is the question, and if it means something, what is it ?

I wonder about the Engineers working on SLC/MLC technology, and what kind of people they are. Do they dream BIG ? I wonder what their big dreams are. Artificial Intelligence that replaces and subjegates us all, for all eternity ?

Wonder if the Egyptians ever thought it would come to THIS.

We may someday spend all eternity in boxes like these. I think it would be a good idea to find out what Heaven is going to look like.


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## BoT (Dec 16, 2008)

if a pattern is long beyond human predictability, would that make it random?
i am sure that SLC/MLC engineers have to think big, at least outside the box.

Although SSD technology has been around for a while, it is still very much in it's baby shoes. there are a lot of improvements to be made and problems to solve. 

the technology as of today, in my opinion can be very forth coming depending on the application they are used in. for example, i think a web server could greatly benefit from SSD's while a file server would probably not have a good look at all with it. 
for the end user, if inet surfing, games and office apps are your primarly pet pee then i think it could work well, i'd also prefer it in a laptop. if you do photo/ video editing, 3d rendering, etc i'd probably stay away.


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## Fren Banklin (Nov 6, 2008)

Okay BoT, I woke up this morning, armed myself with a pot of coffee and finished the marathon AnandTech article on SSD's. And now I know why it is that there is no simple and easy, marketing department-inspired set of numbers to easily compare the "thorughput" of standard HD's to SSD's.

Long list of reason why not. One of them is that the point is to drive manufacturers to continue to push the envelope and improve SSD's at least to the point that their costs are on-par with HD's, while deriving the benefit of the dramatic performance advantages.

I wonder why the Intel X-25 is so expensive ? With OCZ's obvious advent as the leader in the affordable and "good enough" SSD market, does Intel really want to be known as the "expensive" SSD manufacturer ? They can ask whatever they want; but will people pay it ?

I wouldn't.

The JDMicron controller situation was interesting. Seems the manufacturer's were trying to take advantage of the maximum capabilities the new technology would afford, while sacrificing performance in other areas that most people would (and did) find unacceptable.

I have to wonder what OCZ was thinking, when it's firmware jacked the sequential R/W times to 230 Mb/s, while still allowing 1/2 second delays in small and random R/W times ?

And a firmware modification fixed it ?

Hmm. Occurs to me, perhaps OCZ saw it coming. Put out the fact their SSD's were capable of 230 Mb/s throughput, but have been "downclocked" in order to reduce the "stuttering" that occurs during random R/W's.

The OCZ Vertex is the fastest, affordable SSD that doesn't stutter.

Except, when it's not stuttering, it's also not the fastest. VERY convoluted. Any magic number given to describe this situation (which I was carrying on about in the beginning of the thread) would have been dishonest.

Thanks for the article.


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## BoT (Dec 16, 2008)

very welcome. 
it is a good read but as i mentioned, take it with a grain of salt. 
although i would not dar to say that anand is wrong in some of his conclusions i certainly would like to say that i have a difference in opinion in some points.

his test is good and thourought but limited. he is only selecting "his" prefered brands for testing. obviously the intel ssd's wear the performance crown and the ocz vertex is possibly second best, i still don't think that they are in a reasonab;e or affordable range.
to compare them with an, at that point, already outdated and much cheaper JDMicron controller is a bit of the path for me. 
what they say" you get what you pay for". you think there are not many people that would pay the price for intel, certainly they are and anand's article is only helping.
not that i want to deminish his opinion or take credit away from intel's product but it's just about a different class. it's like comparing a ferrari with a honda accord. 

anyway's, reading that article and having used a ssd is two different things. 
i purchased two patriots warp2's, unfortunatly just before they release the warp3 with the new controller. i have been using the drives for a little while now, formated them several times and threw a slew of OS's on them just to erase and start over. 
i run them in raid0 i have to say in all fairness but i could not detect a clear and unmistakable stutter. i haven't tested it yet in a single drive configuration.
these drives are about half of what the intel's go for or i could get two for that price and i still think they are pretty pricy. even compared to WD velociraptor, about the same price but twice the storage on the raptor. 

paying $2+ dollars for high performance storage is pretty high, paying $4+ dollars is not my playing field and not my ballpark no matter how good it is.


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