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Endurance Testing: Write Amplification And Estimated Lifespan

Intel SSD 520 Review: Taking Back The High-End With SandForce
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SandForce's Technology: Very Low Write Amplification

According to SandForce, SSD manufacturers can tweak firmware in a number of different ways. Naturally, then, we were curious to see whether Intel altered the way SandForce's compression technology worked.

Gauging this requires us to calculate write amplification. Usually, we'd need to endure days of testing in order to generate the numbers used for this calculation. Fortunately, all SandForce-based SSDs come with SMART counters for host writes (E9) and NAND writes (F1). Intel's SSD 520 features the same counters, so it's really only a matter of setting up Iometer to write a compressible sequential workload. Once you look them up, it's pretty easy to calculate write amplification: just divide host writes by NAND writes.

128 KB 100% Compressible Sequential Write
1 Hour, QD=1
Intel SSD 520
60 GB
OCZ Vertex 3
60 GB
Host Writes
1258 GB
1301 GB
NAND Writes176 GB
182 GB
Write Amplification
0.13990
.139892


Intel doesn't appear to be changing the behavior of DuraWrite, which is perfectly fine. Though the company says the SSD 520's firmware is completely its own, this particular aspect of the controller is supplied by SandForce in perfect working order, necessitating nothing in the way of tuning.

Now, at a queue depth of one, an SSD with a non-SandForce controller in it always incurs write amplification greater than or equal to one, meaning flash cells wear faster than on a SandForce-based drive. By compressing data, the SSD 520 and its contemporaries are able to write less data and extend overall endurance.

Endurance: Even Better With SandForce's Compression Technology

By minimizing write amplification, endurance is positively impacted. We can't really understate this effect. Don't believe us? Fortunately, you don't have to take our word alone. All of Intel's latest SSDs come with workload counts that allow you to estimate the life-span of your SSD.

Intel S.M.A.R.T. Workload Counters
Purpose
E2
Percentage of Media Wear-out Indicator (MWI) used
E3
Percentage of workload that is read operations
E4Time counter in minutes


Think of Intel's workload counters similar to a car's trip counter. Instead of distance, they measure endurance over time. We apply a three-hour workload to the drive in order to generate enough data to be meaningful.

Before we dive in, we want to clarify a few things so that you don't misinterpret what we're saying here. 

First, the media wear indicator on an SSD counts down from 100 to 1. Because the number of program-erase cycles a NAND cell can withstand is limited, the MWI is designed to facilitate a rough estimate of endurance. In theory, once you reach the end of the counter, the memory's rated P/E cycles have been exhausted, though that's not to say anything bad will happen immediately after.

Second, using workload counters to estimate endurance is still a tenuous measurement (and without running any of our drives down, we're presenting this information academically, rather than practically). Iometer runs so fast and writes so much that we're essentially condensing months worth of activity into hours. Both Micron and Intel estimate that the average desktop user writes between 7-10 GB worth of information per day. So, we're basing our real-world estimates on at least 7 GB of writes by the host.

Finally, P/E-cycle ratings apply to each flash cell. But because larger SSDs employ more NAND, it takes longer to write across all cells. So, they consequently enjoy a higher endurance rating. The numbers below apply to Intel's 60 GB SSD 520, specifically.

Now, we're able to look at the following data without freaking out about SSD longevity. This is really about SandForce's technology and its effect on write amplification, and, in turn, endurance.

Workload Ratio: 35% 128 KB Sequential, 65% 4 KB Random
128 KB Sequential: 66% Reads, 34% Writes
4 KB Random: 66% Reads, 34% Writes
Full Span, QD=1, ~3 Hours
Intel SSD 520
60 GB
Incompressible
Intel SSD 520
60 GB
Compressible
Total Host Writes
211 GB
583 GB
NAND Writes
616 GB
100 GB
Write Amplification
2.9x
0.17x
Percent MWI used (E2)0.078%
0.037%
Endurance Rating For Workload
0.170 Years
0.905 Years
Real-World Endurance Rating Estimate
(7 GB Written Per Day)
5.12 Years
75.37 Years


Presented with completely compressible data, Intel's 60 GB SSD 520 is told to write 583 GB of data, and actually writes 100 GB to flash. This translates into a write amplification of 0.17x. That's downright incredible considering non-SandForce will generally end up with write amplification that looks more like our incompressible workload, where 211 GB of data is written as 616 GB of to the NAND (yielding amplification of 2.9x).

In reality, you'll probably never see either of the extremes presented here. We're taxing the heck out of these SSDs, allowing no idle time for background garbage collection to affect the drive. That's an important process, responsible for further minimizing write amplification. As a result, in normal use, endurance really isn't your indicator of reliability. Again, we're really just trying to illustrate how SandForce's compression technology, which is sometimes maligned for its variable impact on performance, might also help extend endurance for SSD vendors who use lower-binned NAND.

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  • -8 Hide
    Anonymous , February 6, 2012 3:04 PM
    Hmmm, maybe I missed a good excuse, but I'd like to see the Octane in these tests.
  • 2 Hide
    phamhlam , February 6, 2012 3:11 PM
    I love Intel SSD. 128GB for about $210 isn't bad. It is just hard to not chose something like a Corsair GT 120GB that cost $150 with rebate over this. I would always put a Intel SSD in a computer for novice since it is reliable.
  • 3 Hide
    thessdreview , February 6, 2012 3:32 PM
    Nice Review!
  • 0 Hide
    jaquith , February 6, 2012 3:59 PM
    Nice article :) 

    Just need more SSD's to compare, I'd like to see similar tests done with 120GB...180GB...256GB and several more brands. Further, as I mentioned before in the other article please list the exact model numbers and OEM specs including their 4KB IOPS; otherwise folks don't understand the results and if relying on this a purchasing will have in many cases a 4 in 5 chance of selecting the wrong SSD.

    Prior article - http://www.tomshardware.com/reviews/sata-6gbps-performance-sata-3gbps,3110.html
  • -3 Hide
    theuniquegamer , February 6, 2012 3:59 PM
    costly but i think reliability comes at a price. These ssds are best for enterprises . If the price will be little lower then the common user can afford these and get a good reliable ssd.
  • 1 Hide
    danraies , February 6, 2012 5:55 PM
    These prices are lower than I thought. $20-$40 extra (depending on the comparison) for peace-of-mind is not outrageous.
  • 2 Hide
    acku , February 6, 2012 6:02 PM
    carn1xHmmm, maybe I missed a good excuse, but I'd like to see the Octane in these tests.


    We didn't have the Octane on hand in the 256 GB capacity, but we'll be sure to make that side by side comparison down the road.

    phamhlamI love Intel SSD. 128GB for about $210 isn't bad. It is just hard to not chose something like a Corsair GT 120GB that cost $150 with rebate over this. I would always put a Intel SSD in a computer for novice since it is reliable.


    Excellent point. Price is always a fickle thing.

    thessdreviewNice Review!

    Thanks Les. :) 

    jaquithNice article Just need more SSD's to compare, I'd like to see similar tests done with 120GB...180GB...256GB and several more brands. Further, as I mentioned before in the other article please list the exact model numbers and OEM specs including their 4KB IOPS; otherwise folks don't understand the results and if relying on this a purchasing will have in many cases a 4 in 5 chance of selecting the wrong SSD. Prior article - http://www.tomshardware.com/review [...] ,3110.html


    We'll keep that mind for future reviews. However, we already list model and firmware on the test page.

    Cheers,
    Andrew Ku
    TomsHardware.com
  • 6 Hide
    willard , February 6, 2012 6:03 PM
    bildo123Getting out of standby on my HDD is a matter of seconds.

    And with an SSD, your computer comes out of standby faster than your monitors do. Not kidding.
  • 7 Hide
    mrkdilkington , February 6, 2012 6:08 PM
    Anyone else disappointed Intel isn't producing their own high end chipset? Been waiting to upgrade my X25-M for a while now (Intel 320 isn't a big upgrade) but might just go with Samsung.
  • 0 Hide
    boletus , February 6, 2012 6:49 PM
    Good to see Intel throw its hat into the ring for the prosumer market. We should be able to expect performance and out-of-the-box functionality (as opposed to theoretical endurance) for the amount of money these devices cost. As the article repeatedly infers, this has not always been the case to date (although the last year has seen some major kinks worked out). Competition at the mid to upper end of the market will lead to higher expectations.
  • 1 Hide
    universalremonster , February 7, 2012 12:26 AM
    Quote:
    Anyone else disappointed Intel isn't producing their own high end chipset? Been waiting to upgrade my X25-M for a while now (Intel 320 isn't a big upgrade) but might just go with Samsung.


    Yes, I'm with you on that one. I've had an Intel 320 128Gb SSD for quite some time now and have nothing but the greatest things to say about my particular experience with it. I purposely held off from buying the Marvell controller 510 in hopes that the next refresh would have a new Intel made 6Gb controller. One thing I am curious about, does the new 520 still have the Intel Toolbox software with it? I have gotten alot of use out of it with my current drive and would really hate to not have it on a new one.
  • 0 Hide
    acku , February 7, 2012 12:29 AM
    universalremonsterYes, I'm with you on that one. I've had an Intel 320 128Gb SSD for quite some time now and have nothing but the greatest things to say about my particular experience with it. I purposely held off from buying the Marvell controller 510 in hopes that the next refresh would have a new Intel made 6Gb controller. One thing I am curious about, does the new 520 still have the Intel Toolbox software with it? I have gotten alot of use out of it with my current drive and would really hate to not have it on a new one.


    You can use the Toolbox software with the SSD 520. It will however not work with other SF drives.

    Cheers,
    Andrew Ku
    TomsHardware.com
  • 0 Hide
    Anonymous , February 7, 2012 12:47 AM
    Andrew, could you please comment on the encryption capabilities of the new drive. Does it support AES encryption like the Intel 320? Is there an option for pre-boot? Thanks in advance!
  • 2 Hide
    compton , February 7, 2012 3:03 AM
    Andrew,

    Your SSD investigations/reviews/history lessons are Tier 1.


    But I always get curious when Intel starts on and on about how it has the best NAND around. It's not that I even doubt them when they say this, but AFAIK Intel/Micron/IMFT are made and binned in the same place.

    IMFT is supposed to be 49% Intel and 51% Micron-owned. Now both companies' own drives are stocked with what I presume is the best available NAND at that price point, but how did Intel get the reputation of having better NAND? (and if I'm honest, there is at least some evidence that it does). Micron doesn't run around talking up their NAND as much as they should, and this makes me think that the details of the IMFT arrangement are probably pretty strange. In a blind taste test, they taste pretty similar.

    But not all Micron NAND is created equal, nor is Intel's (for example, does Kingston really get Intel's top shelf shtuff?). The IMFT NAND used in so many drives today runs the gamut from fantastic down to mediocre, only one step above Hynix's too-dirty-for-television flash. I'm probably the one person on this planet that wants to know more about Intel, Micron, and their bastard love child, IMFT.
  • 0 Hide
    nikorr , February 7, 2012 4:15 AM
    So, does this SandForce's SF-2281 controller has the bug as well?

    Or it is already fixed?

    Or they have replaced it with a new version?
  • 0 Hide
    dragonsqrrl , February 7, 2012 6:11 AM
    nikorrSo, does this SandForce's SF-2281 controller has the bug as well?

    As far as Anand can tell... no.

    http://www.anandtech.com/show/5508/intel-ssd-520-review-cherryville-brings-reliability-to-sandforce


    Intel's SF2281 implementation seems to be stable, and BSOD free.

  • 1 Hide
    DjEaZy , February 7, 2012 8:38 AM
    ... my OCZ Vertex 3 is still strong...
  • 0 Hide
    triny , February 7, 2012 9:00 AM
    I have a crucial 128 my next will be Samsung
  • 2 Hide
    TEAMSWITCHER , February 7, 2012 11:44 AM
    Thank you for the OS X benchmarks! There are real differences between Windows 7 and OS X and having these benchmarks helps Mac users make better upgrade decisions.
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