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Understanding SSD Advertised Performance and Its Purchase Implications – An SSD Primer

Understanding SSDs Performance and Implications

Today’s SSD close up is going to teach us the most valuable thing we can ever learn about an SSD.

This is the fourth paper in a series of articles that explain the benefits, types and components of a solid state drive and will go so far as to make up our SSD Beginners Guide . Each article is designed to be easily understood and will enable the reader to become proficient in every aspect of the SSD as it relates to their specific computing needs.

INTRODUCTION

Learning of a new technology and what it can do for us as consumers is somewhat similar to walking into a room blindfolded only to learn that the lights are out once the blindfold has been removed.  Try to find the light switch now right?  The world of solid state drives is no different as many are now buying Ultrabook computers only to have to come here to learn what an SSD is and why their new system hasn’t any hard drive.  Then again many may be here having an idea and hoping to migrate from a hard drive to an SSD.

Solid state drives are an amazingly fast move forward in the world of computers and, unfortunately, their purchase is much the same as we described above where consumers purchase blindly based on high performance numbers that they will never use.  This article is written to dispel the fallacies of ‘high sequential’ speed advertisement and help you along with a key SSD performance speed that you should be looking at in your SSD purchase, the one that will demonstrate very visible computer upgrade.

We are not exaggerating when we state that this is probably going to be the single most important piece of information you will ever learn about solid state drives.

THE SSD MANUFACTURERS BLUFF

Lets get right to the point shall we?  Take a little look at these performance scores and tell me what SSD  you would buy.
Ok… A few of you got it but I am disappointed in most so, lets try again.  Look carefully at the left performance results below and then the right.  Which setup would you believe will result in faster visible performance for the typical user?


Thorough examination should have resulted with your selection of the result on the right. No? I know, I know¦ Some of you are about to write me off as a lunatic and and find another article to help out with your purchase and, in fact, I even cheated a bit by using the performance score of an old RAID configuration to serve my purpose a bit further.  I’ll make you a deal.

Give me just a few minutes and I will change your mind completely  to the way you look at the performance of a solid state drive.

TYPICAL COMPUTER USE AND TRANSFER SPEEDS

When first considering the purchase of an SSD, most will immediately look at performance specifications in order to determine what SSD is best. Unknowingly, they will quickly choose in awe of lightning fast speeds such as 550MB/s read and 520MB/s write that we are seeing in today’s solid state drives. After all, a SSD with a speed of 520MB/s must be faster than one capable of only 415MB/s right?

The answer is both yes and no.  A bit of an understanding of disk access percentages is necessary to be able to intelligently decide specifically what SSD is best for you.  Many may have seen an older version of this article where the disk access results were slightly different than we see below.  I believed it imperative to attain my own test sample and the following results were attained at the time of this article.

Top 5 Most Frequent Drive Accesses by Type and Percentage:

  • -4 Read (8%)
  • -4K Write (58%)
  • -512b Write (5%)
  • -8k Write (6%)
  • -32k Read (5%)

Top 5 account for: 80% of total drive access over test period

Largest access size in top 50:256K Read (-1% of total)

Using Microsofts Diskmon, I simply monitored my typical computer usage in doing things such as using the internet, running applications, playing music etc.  In short, I did my best to recreate the computer use of a typical user and then used the program to break down the percentage that specific disk transfer speeds were being utilized. The above results were calculated through a ten minute test period during which results were supplied throughout the test.  This is a simple test that anyone could recreate once they have downloaded the software.

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Frank
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Frank

This is a very interesting test. It does indeed shed light on a fallacy of typical SSD advertising. One other thing it sheds light on is even more surprising. How wasteful the OS is of write cycles. Look at the numbers again. 56.53% of all accesses in his test were 8K writes. 8K reads were nuber 2 at only 7.6%. When is the computer reading all of this data that it is writing? If you do some math on the full results does it show something closer to balance in total K read versus total K written? Given that JEDEC… Read more »

Nick
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Nick

I certainly agree with you on principle, but I wonder how much of that data could be writes to the same block. Consider a program with a while loop and a counter. If I only care about the value of the counter after the while loop’s exit condition is met, I may potentially be writing a value there many times before a single read is needed. Surely other similar situations also exist. (Granted, in this trivial case, that information need not be stored to disk.)

Molgor
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Molgor

Also keep in mind that PCs are running more and more .Net applications, not to mention Windows, Office, and other Microsoft Software. At least some of the code, if not half or more, is MSIL, not machine language. As the CLR interprets the MSIL, it is constantly upgrading the code to Native Mode. That could account for some of the 8K writes as well.

David
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David

I would love to hear your analysis and recommendations on using a RAM disk in conjunction with an SSD. I’m doing that now and have installed my two most write-intensive applications (stock charting and anti-virus) into it as well as locating my web browser caches (IE and Firefox) and user temp file locations into it. I’m using DataRam’s free RAMDisk driver.
I bring this up as I’ve read that Windows 7 caches much of what’s in RAM on the disk anyway – thus negating my “protecting” my SSD from the writes of applications writing to the RAMDisk.

Q
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Q

Not sure on Win7, but I assume it shouldn’t be much different… In WinXP, for something like 4 years or so, I disabled the paging file altogether. What this means are 2 things: 1 – (the bad) if you do not have enough RAM windows will simply tell you so and if you use more, one of the programs will get closed. Nowadays 4Gb should take care of most (95%) of situations, 8Gb if 4Gb doesn’t cut it will solve your problems; 2 – (the great) Never again will windows copy something out of the RAM into the disk in… Read more »

Sam
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Q, I had my paging file disabled for a long time, too. In the end, I did some measurements, and was quite surprised: while I felt good having the paging file disabled, it actually did nothing for my computers performance. In the end I did not bother disabling it after the last reinstall, since it does not help measured performance in any way, and instead can pose problems if you run out of memory. SITE RESPONSE: I have been the biggest advocate of ‘no pagefile’ for years and have never said that it alone will increase performance. I have also… Read more »

Trane Francks
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Q: It’s important to note that a 32-bit Windows system cannot use more than 4 GB of RAM, even with Physical Address Extension enabled. As such, your 8 GB suggestion wouldn’t improve things at all unless the user also upgraded to a 64-bit OS. Even then, the Windows 7 Starter version is limited to 2 GB RAM.

Gonzo_V
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Gonzo_V

WOW… now I am noways close to even writing code much less really knowing exactly where and the inter reaction too all the terms you used to explain your view of the subject. However I did understand what you were talking about in terms of it’s actual event/product to the operating system……….thanks guys really insightful.

Gonzo

SITE RESPONSE: Thank you for the favorable return.

wx4sno
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wx4sno

The 4k read chart above, was that conducted on 34nm or 25nm NAND? I’ve heard recently that the OCZ Vertex 2 has been shipping with 25nm and everyone is reporting much slower response times…your thoughts??? I just bought a Vertex 2 but I don’t know if it will arrive as 34nm or 25nm….