A Wear Leveling Refresher: How Long Will My SSD Last?

As if everything I’ve talked about thus far wasn’t enough to deal with, there’s one more major issue that directly impacts the performance of these drives: wear leveling.

Each MLC NAND cell can be erased ~10,000 times before it stops reliably holding charge. You can switch to SLC flash and up that figure to 100,000, but your cost just went up 2x. For these drives to succeed in the consumer space and do it quickly, it must be using MLC flash.


SLC (left) vs. MLC (right) flash

Ten thousand erase/write cycles isn’t much, yet SSD makers are guaranteeing their drives for anywhere from 1 - 10 years. On top of that, SSD makers across the board are calling their drives more reliable than conventional hard drives.

The only way any of this is possible is by some clever algorithms and banking on the fact that desktop users don’t do a whole lot of writing to their drives.

Think about your primary hard drive. How often do you fill it to capacity, erase and start over again? Intel estimates that even if you wrote 20GB of data to your drive per day, its X25-M would be able to last you at least 5 years. Realistically, that’s a value far higher than you’ll use consistently.

My personal desktop saw about 100GB worth of writes (whether from the OS or elsewhere) to my SSD and my data drive over the past 14 days. That’s a bit over 7GB per day of writes. Let’s do some basic math:

  My SSD
NAND Flash Capacity 256 GB
Formatted Capacity in the OS 238.15 GB
Available Space After OS and Apps 185.55 GB
Spare Area 17.85 GB

 

If I never install another application and just go about my business, my drive has 203.4GB of space to spread out those 7GB of writes per day. That means in roughly 29 days my SSD, if it wear levels perfectly, I will have written to every single available flash block on my drive. Tack on another 7 days if the drive is smart enough to move my static data around to wear level even more properly. So we’re at approximately 36 days before I exhaust one out of my ~10,000 write cycles. Multiply that out and it would take 360,000 days of using my machine the way I have been for the past two weeks for all of my NAND to wear out; once again, assuming perfect wear leveling. That’s 986 years. Your NAND flash cells will actually lose their charge well before that time comes, in about 10 years.

This assumes a perfectly wear leveled drive, but as you can already guess - that’s not exactly possible.

Write amplification ensures that while my OS may be writing 7GB per day to my drive, the drive itself is writing more than 7GB to its flash. Remember, writing to a full block will require a read-modify-write. Worst case scenario, I go to write 4KB and my SSD controller has to read 512KB, modify 4KB, write 512KB and erase a whole block. While I should’ve only taken up one write cycle for 2048 MLC NAND flash cells, I will have instead knocked off a single write cycle for 262,144 cells.

You can optimize strictly for wear leveling, but that comes at the expense of performance.

Why SSDs Care About What You Write: Fragmentation & Write Combining Why Does My 80GB Drive Appear as 74.5GB? Understanding Spare Area
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  • tachi1247 - Friday, September 18, 2009 - link

    Does anyone know what the difference is between the 7mm thick and 9.5mm thick drives?

    http://download.intel.com/design/flash/nand/mainst...">http://download.intel.com/design/flash/nand/mainst...

    They seem to be identical except for the drive thickness.
    Reply
  • dszc - Saturday, September 12, 2009 - link

    FANTASTIC series of articles. Kudos! They go a long way toward satisfying my intellectual curiosity.

    But now it is time to reap the rewards of this technology and earn a living.
    So I need some real-world HELP.

    How do I clone my 320GB (80GB used) Hitachi OS drive (Vista 32 SP2) over to a 128GB Indilinx Torqx?

    All I really care about is Photoshop and Bridge CS4 performance. I am a pro and work 4-16 hours per day in Bridge and Photoshop, with tens of thousands of images, including 500MB - 2GB layered TIFFs. The Photoshop Scratch Disk and Bridge and CameraRaw Cache performance are killing me. Solid State Storage seems to be the perfect solution to my problem

    I really want to simply clone my 320 over to the Torqx, because it would take me a week to re-install and configure all of my software and settings that are now on the 320GB Hitachi.

    Do I just bring the Torqx up in the Vista Storage Disk Management, initialize it with one big partition, and then format it?
    What size allocation unit should I use? :
    Default? 4096? 64k? ???
    Will these settings be wiped out when I clone over the stuff from the old hard drive?
    What about "alignment"?
    What is the best software for a SIMPLE & painless clone procedure?

    I'm not a techie or geek, but have a fair working knowledge of computers.

    Any help would be hugely appreciated. Thanks.
    Reply
  • userwhat - Thursday, September 17, 2009 - link

    I use Drive Snapshot for all these purposes. It works 100%, it´s a very small and fast program. After having issues with Norton Ghost and some other similar programs which were absolutely unable to restore an imaged partition stored on a DVD this is THE one to use.

    Get it here: http://www.drivesnapshot.de/en/">http://www.drivesnapshot.de/en/
    Reply
  • dszc - Saturday, September 26, 2009 - link

    Thank you very much for your help and recommendations.
    To get my Patriot (SolidStateStorage) up and running, I used Seagate DiskWizard (an Acronis subset), as I have lots of Seagate drives already on my system and this free software seems to work.
    When I get a window of time in my schedule, I'll try DriveSnapShot and/or DriveImage to see if they do a better job in helping my Torqx SSS run at its full potential.
    Thanks again for your help.
    Dave
    Reply
  • JakFrost - Tuesday, September 15, 2009 - link

    If you want to image out your current drive and migrate over to an SSD you can use the free software below that works with Windows Volume Shadow Copies to do a online live migration to another drive without losing or corrupting your data. This means that you can do this from the same OS that you are running.

    This software will allow you to image out to an already created partition that is already aligned at the 1MB boundry that is standard for Microsoft Vista/7 operating systems.

    DriveImage XML V2.11
    English (1.78MB)

    Image and Backup logical Drives and Partitions

    Price: Private Edition Free - Commercial Edition - Buy Now Go!
    System Requirements: Pentium Processor - 256 MB RAM
    Windows XP, 2003, Vista, or Windows 7

    An alternative is to use an offline migration system such as Acronis TrueImage, Norton Ghost, etc. to do the migration offline from a bootable CD or USB drive. Search around for Hiren's BootCD to check out these and other tools to do the migration.
    Reply
  • dszc - Saturday, September 26, 2009 - link

    Thank you very much for your help and recommendations.
    To get my Patriot (SolidStateStorage) up and running, I used Seagate DiskWizard (an Acronis subset), as I have lots of Seagate drives already on my system and this free software seems to work.
    When I get a window of time in my schedule, I'll try DriveImage and/or DriveSnapShot to see if they do a better job in helping my Torqx SSS run at its full potential.
    Thanks again for your help.
    Dave
    Reply
  • jgehrcke - Friday, September 11, 2009 - link

    Be careful when buying a Super Talent UltraDrive GX 128 GB with "XXXX" in serial number (unfortunately you cannot check this before ordering the drive). These drives are much slower than measured in the benchmark here and in other benchmarks.

    For more information and related links see

    http://gehrcke.de/2009/09/performance-issue-with-n...">http://gehrcke.de/2009/09/performance-i...est-supe...
    Reply
  • Kitohru - Thursday, September 10, 2009 - link

    Does OS X Snow Leopard have trim support, and if not any word from apple about that or the like? Reply
  • Zool - Thursday, September 10, 2009 - link

    I still dont think that with this price ssd-s will be more mainstream in the next years. And honestly the performance is not even that extra if everything would work like it should. The mechanical drives can reach now 100 MB reads when things are optimal. The small files performance is still only software problem. U should never ever reach point when u need to randomly find 4 KB files in a long row. With todays ram capacity and cpus-s programs should never read such small files or group things in larger files and read whole to memmory. A solid today programed aplication (let it be game or programs) should never let your disk spam with 30k files (like catia or other plenty of aged so called "profesional" programs). With today ram and disk capacity it should read things to memmory and let only grouped larger files on disk and never ever touch the hdd again until users isnt comunicating with the software (u can tell it to windows).Saves can be made to memmory and than write to disk without even seeing a fps drop in games(not just games) becouse of disk comunication latenci
    I dont even think the IO performance would be a problem with the RIGHT software and OS. With 100MB reads it could run perfectly fine with few seconds loading times. Even the latencies of ssd-s are no match to ram latencies so everithing that should activly comunicate with disks (which is just stupid with curent ram prices and 64bit) would just level your latencies down to disks.
    Why should worry about latencies and read speeds when u could copy it to ram and keep the files on disk in shape where the mechanical drive
    should never find itself to read files smaller than few MB.(even your
    small txt documents u can hide in archive).
    Just my toughs. (sorry for my english)
    Reply
  • AlExAkE - Wednesday, September 09, 2009 - link

    Hey, I'm a web & multimedia designer. I spend lots of my time using most of the Adobe CS4 products including Photoshop, Flash, Dreamweaver, Illustrator, After Effects & Premiere Pro.

    The Intel 80GB G2 looks amazing, but the Photoshop test is awful because of his write speed. The Intel 25-Extreme series seem to be the best but is to pricey. The OCZ Vertex has good write speed but is slower than Intel G2 in most of the test. What would be the recommended SSD for my purpose. Thanks
    Reply

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