The Instruction That Changes (almost) Everything: TRIM

TRIM is an interesting command. It lets the SSD prioritize blocks for cleaning. In the example I used before, a block is cleaned only when the drive runs out of places to write things and has to dip into its spare area. With TRIM, if you delete a file, the OS sends a TRIM command to the drive along with the associated LBAs that are no longer needed. The TRIM command tells the drive that it can schedule those blocks for cleaning and add them to the pool of replacement blocks.

A used SSD will only have its spare area to use as a scratch pad for moving data around; on most consumer drives that’s around 7%. Take a look at this graph from a study IBM did on SSD performance:

Write Amplification vs. Spare Area, courtesy of IBM Zurich Research Laboratory

Note how dramatically write amplification goes down when you increase the percentage of spare area the drive has. In order to get down to a write amplification factor of 1 our spare area needs to be somewhere in the 10 - 30% range, depending on how much of the data on our drive is static.

Remember our pool of replacement blocks? This graph actually assumes that we have multiple pools of replacement blocks. One for frequently changing data (e.g. file tables, pagefile, other random writes) and one for static data (e.g. installed applications, data). If the SSD controller only implements a single pool of replacement blocks, the spare area requirements are much higher:

Write Amplification vs. Spare Area, courtesy of IBM Zurich Research Laboratory

We’re looking at a minimum of 30% spare area for this simpler algorithm. Some models don’t even drop down to 1.0x write amplification.

But remember, today’s consumer drives only ship with roughly 6 - 7% spare area on them. That’s under the 10% minimum even from our more sophisticated controller example. By comparison, the enterprise SSDs like Intel’s X25-E ship with more spare area - in this case 20%.

What TRIM does is help give well architected controllers like that in the X25-M more spare area. Space you’re not using on the drive, space that has been TRIMed, can now be used in the pool of replacement blocks. And as IBM’s study shows, that can go a long way to improving performance depending on your workload.

Why Does My 80GB Drive Appear as 74.5GB? Understanding Spare Area Tying it All Together: SSD Performance Degradation


View All Comments

  • CList - Tuesday, September 01, 2009 - link

    Don't be disgusted at Newegg, be disgusted at the people who are willing to pay the premium price! Newegg is simply playing a reactionary role in the course of natural free-market economics and cannot be blamed. The consumers, on the other hand, are willing participants and are choosing to pay those prices. When no one is left who is willing to pay those prices, Newegg will quickly lower them.

  • gfody - Tuesday, September 01, 2009 - link

    I don't understand how consumers have any control over what Newegg is charging for the 160gb that's not even in stock yet.

    If Newegg wants to get the absolute most anyone is willing to pay for every piece of merchandise they may as well just move to an auction format.
  • DrLudvig - Tuesday, September 01, 2009 - link

    Yeah, if you look at intel's website,">, you will se that the R5 includes "3.5" desktop drive bay adapter to 2.5" SSD adapter bracket, screws, installation guide, and warranty documentation.
    Why on earth Newegg is charging that much more for it i really don't know, here in denmark the R5 retails for about 15 bucks more than the C1.. Which really isn't that bad..
  • Mr Perfect - Tuesday, September 01, 2009 - link

    Whoa. That's it? An adapter kit? With that kind of price difference, I expected it to be the D0 stepping of SSDs or something.

    Thanks for clearing that up.
  • NA1NSXR - Monday, August 31, 2009 - link

    The reason not being that performance or longevity is not good enough, but because improvements are still coming too quickly, and prices falling fast still. Once the frequency of significant improvements and price drops slow down, I will more seriously consider an SSD. I suppose it depends on how much waiting on the I/O you do though. For me, it is not so much that a Velociraptor is intolerable. Reply
  • bji - Tuesday, September 01, 2009 - link

    Perhaps this is what you meant, but you should really clarify. It's still not time for YOU to buy an SSD. SSDs represent an incredible performance improvement that is well worth the money for many people.
  • DragonReborn - Monday, August 31, 2009 - link

    say i wanted to go crazy (it happens)...should i get two 80gb intel g2's or the 160gb intel g2? same the RAID 0 performance worth it?

    i have all my important data backed on a big 2tb drive so the two ssd's (or 1 160gb) will just hold my OS/progs/etc.

  • kensiko - Monday, August 31, 2009 - link

    I would say that in real world usage, you won't notice a huge difference between RAID and not RAID, SSD are already fast enough for the rest of the system. Also, TRIM may not work for now in RAID configuration.

    Just look at Windows Start up, no difference between Gen2 SSD!
  • Gc - Monday, August 31, 2009 - link

    This is a nice article, but the numbers leave an open question.
    What is Samsung doing right? Multiprocess/multithread performance?

    The article finds Samsung drives performance is low on 2MB reads,

    (new 2MB sequential reads not given, assume same as 'used')
    used 2MB sequential reads (low rank, 79% of top)

    good on 2MB writes:

    new 2MB sequential writes (middle rank, 89% of top)
    used 2MB sequential writes (2nd place, 91% of top)

    and horrible on 4KB random files:

    (new 4KB random reads not given, assume same as 'used')
    used 4KB random read (bottom ssd ranked, only 36% of top)
    new 4KB random write (low rank, only 9% of top)
    used 4KB random write (bottom ssd ranked, only 3% of top, < HD)

    Yet somehow in the multitasking Productivity test and Gaming test, it was surprisingly competitive:

    multitasking productivity (mid-high rank, 88% of top)
    gaming (mid-high rank, 95% of top)

    The productivity test is described as "four tasks going on at once, searching through Windows contacts, searching through Windows Mail, browsing multiple webpages in IE7 and loading applications". In other words, nearly all READS (except maybe for occasionally writing to disk new items for the browser history or cache).

    The gaming test is described as "reading textures and loading level data", again nearly all READS.

    Q. Given that the Samsung controller's 2MB read performance and
    4KB read performance are both at the bottom of the pack, how
    did it come out so high in the read-mostly productivity test
    and gaming test?

    Does this indicate the Samsung controllers might be better than Indilinx for multiprocess/multithreaded loads?

    (The Futuremark pdf indicates Productivity 2 is the only test with 4 simultaneous tasks, and doesn't say whether the browser tabs load concurrently. The Gaming 2 test is multithreaded with up to 16 threads. [The Samsung controller also ranks well on the communications test, but that may be explained: Communications 1 includes encryption and decompression tasks where Samsung's good sequential write performance might shine.])

    Since many notebooks/laptops are used primarily for multitasking productivity (students, "office"-work), maybe the Samsung was a reasonable choice for notebook/laptop OEMs. Also, in these uses the cpu and drive are idle much of the time, so the Samsung best rank on idle power looks good. (But inability to upgrade firmware is bad.)

    (The article doesn't explain what the load was in the load drive test, though it says the power drops by half if the test is switched to random writes; maybe it was sequential writes for peak power consumption. It would have been helpful to see the power consumption rankings for read-mostly loads.)

  • rcocchiararo - Monday, August 31, 2009 - link

    Your prices are way off, newegg is charging ludicrous ammounts right now :(

    also, the 128 agility was 269 last week, i was super exited, then it went back to 329, and its now 309.

Log in

Don't have an account? Sign up now