SSD 102: The Ins And Outs Of Solid State Storage

Some Numbers: Performance and Power Consumption

There is no alternative to studying reviews and comparing comparative information before purchasing SSDs, especially if you’re looking for a larger number of drives for servers. All manufacturers promise 230+ MB/s and 180+ MB/s read and write throughput, as well as thousands of I/O operations per second for their drives. While most products deliver on these expectations when it comes to peak performance, the minimum and average performance numbers can be significantly lower. This means that you should always be planning with minimum performance numbers in an effort to avoid issues in your business environment. In the end, a drive that usually writes at around 200 MB/s will still be unsuitable for high-performance environments, even if it might drop to 40 MB/s here and there.

I/O Enables Our Digital Lives

Eventually, it does not matter too much whether an SSD reads at 220 or at 250 MB/s, or if it writes at 210 or 180 MB/s. Only hardcore enthusiasts will be able to tell a difference. However, SSDs make much more of a difference in enterprise scenarios where ridiculous amounts of I/O operations per second are way more important than throughput.

If you think about how many users log on to Web services at any point in time, you'll realize that we’re discussing a number of I/Os that no one can grasp anymore. Facebook alone reputedly has some 400 million active users, and each of their login requests trigger many read and write operations. Despite this massive traffic, we still expect immediate responses to all of our clicks and requests. Now consider how your digital footprint spreads: logins across various Web sites, analytics, tracking, reposts by other users, on and on. You get the point. We need SSD-class performance to help manage this data avalanche.

Power Consumption

The same thinking applies to power consumption. Why should we care if drives with less than 0.1 W idle power go from 2 W to 1.5 W from one SSD generation to the next? With laptops, this is indeed mainly relevant only for road warriors who want maximum battery runtime. But from a global perspective, especially including data centers, each watt can matter. According to IDC, servers worth $42.2 billion were purchased in 2009. The cost for power required to operate those servers was $32.6 billion. Every watt of power required to run data center hardware requires 2.5 W of additional power for cooling.

Where To Go?

Clearly, the metrics are changing. Whereas companies used to look at gigabytes or performance per dollar, today's managers are more interested in I/Os per dollar, I/Os per watt, and sometimes gigabytes per watt. These metrics clearly favor of SSDs. In the end, what matters is expanding data center performance and capacity without physically expanding the data center itself.

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26 comments
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  • LaloFG
    Very good article; times of most affordable capacity in SSD units is coming...
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  • Lewis57
    A very good article. I love these articles explaining everything. I'm planning on buying two OCZ Vertex 2E 60GB for RAID-0 when I get enough money. Can't wait, should be one hell of an upgrade from a single 5400rpm WD green drive.
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  • ares1214
    Memristors might make SSD's sorter lived than people thought, but who knows. Great article btw.
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  • JoeSchmuck
    From what I understand, TRIM is supported under IDE mode using Win7 as well so you do not need AHCI. I have a Samsung’s VBM19C1Q firmware device and running IDE mode.
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  • hemburger
    Great article!! :D
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  • Anonymous
    Earlier this year we deployed a 5 node failover cluster with iSCSI backend. Each of the VM Host servers utilize a pair of solid state drives for booting and operating, with VM's running off of iSCSI shared cluster volumes. The servers are unbelievably fast and stable - 6 months of 100% uptime on Windows 2008R2. We only use magnetic HDD's now for transporting backups off site.
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  • Anonymous
    One thing that I'm very curious, if we follow Tomshardware's advice to turn off disk defragmentation, the files on SSD would be defragmented over time.

    Upon SSD data loss, can we recover the data files if it's defragmented, especially on a SSD that has never been defragmented as Tomshardware had recommended?
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  • randomizer
    Defragmentation of an SSD is not entirely unnecessary. It's important to distinguish between file fragmentation and free space fragmentation. The former is not an issue with SSDs because all parts of an SSD can be read at the same rate (the same is true for writing if the blocks are clean). But fragmentation of free space, whereby free space is largely distributed across partially-filled blocks, can severely reduce the performance of an SSD. Any time a file of <512kB is written to an SSD, it will take up only part of a block. However, the SSD will eventually run out of clean blocks and will need to re-arrange the data by erasing partially-filled blocks and consolidating them to free up more blocks for further writing. Running a free space defragmentation on the drive will aggressively consolidate the data on-demand so that you don't have the problem occurring when you didn't plan for it.

    Most SSDs will perform this process themselves when idle for extended periods, but it happens at a slow rate. This is what most manufacturers refer to when they talk about Garbage Collection.
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  • Alvin Smith
    Please send me the four fastest 256GB SSDs on the market, so that I might perform my own comparison ... I'll just sit by the door and wait for UPS to arrive.

    Thanks, in advance !!

    = Alvin =
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  • gordonaus
    I put an SSD in my new computer and it was good but after i got the firmware update and changed to AHCI it was AMAZING (OZC Vertex 2 60gb). I would say tho that 60 gb is not enough, i installed windows photoshop and a few other design programs and i only have 20GB left
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  • compton
    Great article. I'm happy to see it in the mix. I'm sticking with my Intel x25-V and OCZ Agility 60 for a little while, but who knows what the future will bring.
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  • cadder
    I haven't seen this addressed before- how does the reliability and data safety of an SSD compare to a mechanical hard drive?
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  • Anonymous
    It is much cheaper to buy 2 Hitachi 7200K disks which are quite reliable and compact RAID enclosure like Jou Jye. And you can have same SSD performance with 1TB drive for the price of one 256GB SSD. I have to mention that I can have up to 2,5Gbps max transfer rate which is not far from SATA II limit.
    I am using same configuration on desktop. What I have noticed is that performance is actually much better than I expected. That is probably because of cache memory. If you have drives with big cache then in RAID stripe configuration those caches logically combine. In case of good desktop drive you can easily have 64MB cache. BTW I looked at the SSD drives caches - wow I know where performance comes from. :) Actually not from SSD technology as such.

    I think SSD is overrated right now. They have to be 4x cheaper. Otherwise it makes no sense. Next year they will be 2x cheaper and after one more year they will 2x more cheaper. So actually technology still needs two years to be usable.

    My recommendation: stick to SATA and RAID - save the money. If you need little storage and max comfort then use SSD.
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  • d1rtyju1c3
    This was a great article. I learned alot of new thing I never knew about SSD's. Now I will be able to make a better selection when I add a SSD.
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  • Keeper
    dvdeo,

    You save a lot of money with SSDs, simply because their watt consumption is really low. So, in long term (say 1y) you will be saving enough money to probably buy those Hitachi 7200K for free.

    Energy efficiency is the key factor with SSDs.
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  • JoeSchmuck
    I understand data reliability for SSD cells that may have reached thier maximum writing number, that the cells can still be read making the data at least available which is much better than a mechanical hard drive since when they fail, ut's usually not good.
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  • bitterman0
    Keeper... So, in long term (say 1y) you will be saving enough money to probably buy those Hitachi 7200K for free...

    The power consumption difference of a single drive is negligible for the purposes of generating any tangible savings on the electric bill. Let's assume the average power consumption difference between HDD and SSD is 5W, and the system that employs the drive is up 24/7/365. Also, let's assume that your electricity cost is 14 cents per kWh (that's what I'm paying on average, your mileage may vary). Thus 0.005kW * 24h * 365d * $0.14 = $6.132 - that's your annual savings (to be clear, that's six dollars and some change, not six thousand). Surely, if you employ hundreds upon hundreds of drives, the savings will add up, but in the end the up-front investment into SSD's higher cost is not likely to pay off within the SSD lifetime, not to mention to get you any savings.

    On a separate note, I do believe that longevity of drives is one of the major factors that affects the purchase decision. For enterprise use, if the drive is constantly hammered by writes (say, a database file is stored on it), the rate of wearing out re-writable flash is likely to be higher than the rate of failure of magnetic drives (certain 10K RPM IDE drives notwithstanding).

    ... if only SSD were more affordable! But, perhaps, the rumored adoption of 2Xnm technology for NAND by Intel by the end of this year will finally put enough pressure on the market to bring down prices to the realm of affordability. One can only hope.
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  • doorspawn
    Can someone shed some light on a query I'm sure many of us have here:

    Why is the block size so large?
    What makes a 4KB or even 256B block a bad idea?
    Is it there's a large per-block component that can't be shrunk?
    Is it that blocks need to be insulated from each other so that high-voltage instructions (perhaps clear) don't leak?
    Those are purely guesses.
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  • Anonymous
    Good overview article, error on last graph:
    5.5 watts to 1.7 watts is not "1/3 Reduced" as per label - it is "2/3 reduced" or "Reduced to a 1/3"
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  • dEAne
    thanks for this article.
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