Solid State Drives 101: Separating the Facts from the Myths

Solid State Drives — SSDs — are getting more popular every day in the world of computing, both in individual devices like the Mac and in enterprise data storage. There are still some people and companies that refuse to take advantage of the many benefits that SSDs have over their slower mechanical counterparts — Hard Disk Drives (HDDs) — because of misconceptions about how the faster, all-electronic SSDs work. In this post, we’ll dispel some of those myths with cold, hard facts.

Myth Number 1: SSD Prices Are Incredibly High Compared To HDDs
When SSDs first appeared on the market, the cost per gigabyte of SSD storage was a lot more than equivalent HDDs. Since that time, the flash memory technology used in SSDs has matured and prices have dropped a lot. But the fact remains that this “myth” is partially true – prices are still higher.

However, when considered for use in enterprise storage situations, other factors like greater storage density, decreased power consumption, and greater reliability can make SSD overall costs lower than those associated with HDDs. For personal use, the increased speed of an SSD, completely quiet operation, and ability to survive drops that would damage an HDD are other benefits that can make the extra cost worthwhile. Current trends show SSD prices decreasing at a faster rate than those of HDDs, so it’s reasonable to assume that the myth will be fully “busted” in a few short years.

Myth Number 2: SSDs Get Slower Over Time
The flash memory chips used in SSDs use a different method of writing data to the drive. On an HDD, it’s possible for a drive to simply overwrite data that was stored previously and that has been marked as “deleted”. SSDs can’t do this — any location that the drive wishes to write to has to be completely erased before it’s possible to commit the writing of data.

This means that SSDs have traditionally been at their fastest fresh out of the box when none of the blocks have to be erased prior to being written to. As more and more data is written to the drive, those erased blocks become few and far between, meaning that the drive has to erase a block before it can be written to and slowing down performance.

However, that was the case a few years ago — not now. Today’s SSD products take care of this issue by doing “garbage collection” in background to erase previously used blocks. When a write request is received by the drive, the blocks are available to be written to and there’s no slowdown over time.

Another mitigating factor with current drives is that they’re often overprovisioned beyond the advertised capacity to provide more empty space, meaning that fewer erase cycles are required and keeping speeds steady over time. In the past, SSD manufacturers often rated their drive specifications based on their “fresh out of the box” performance; now, published specifications usually reflect actual production conditions and are much more accurate over the lifetime of the drive. Further Reading: With An OWC SSD, There’s No Need For TRIM

Myth Number 3: SSDs Don’t Last As Long As HDDs
Sadly, no storage lasts forever, but a report from the Storage Networking Industry Association (SNIA) from as long ago as 2011 showed a MTBF (mean time between failures) for SSDs that was over twice a large as that for HDDs — 2.1 million hours compared to 1 million hours. Current data from SSD manufacturer Samsung shows similar MTBF information, and reliability that is so good that the company can offer a 10 year warranty on its SSDs compared to a standard 2 year warranty on HDDs.

MTBF numbers, however, can be misleading as they assume a perfect world situation in which a drive is sitting quietly in a perfectly-controlled lab environment and really tell you nothing about real-life reliability As mentioned earlier, SSDs can survive impacts that would destroy a HDD, so something as commonplace as dropping or bumping an HDD — even one that is “parked” — can result in a failure while an SSD would brush off the drop as if nothing happened.

Closeup of a wafer of Micron's 3D NAND dies, used in SSDs. Image via Micron.

(Closeup of a wafer of Micron’s 3D NAND dies, used in SSDs. Image via Micron.)

Myth Number 4: SSD Capacities Are Less Than HDDs
This used to be very true…but not any more! New technologies have been adopted by SSD manufacturers and the result are huge drives, usually used in enterprise situations. For example, see the OWC ThunderBay 4 mini with 4 x 10TB SSDs! The capacity myth has been shattered, and it’s generally believed that the laws of physics make anything larger than a 40TB drive an impossibility. For now, at least, SSD capacities can continue to grow as new solid-state storage breakthroughs are made.

Myth Number 5: SSDs Are Only Useful In High Performance Computing Workloads
SSDs are incredibly fast when compared to HDDs. Since HDDs use mechanical actuator arms that must be moved to a precise location on a spinning platter in order to read or write data, there’s a limit to how fast the platters can spin and how fast the actuators can move the arms.

SSDs have no moving parts, made up of semiconductors that can access storage locations instantaneously. As an example of just how fast SSDs are in comparison to HDDs, we need only look at the number of input/output operations per second (IOPS) each can achieve. A top-of-the-line enterprise HDD spinning at 15,000 RPM maxes out at about 180 IOPS. Take a look at an enterprise SSD, and they’re generally able to reach up to 200,000 IOPS — roughly three orders of magnitude faster.

I personally see an example of just how fast SSDs are when I switch between my late 2015 27-inch Retina iMac (2.12 TB Fusion Drive) and my mid-2017 13-inch MacBook Pro with Touch Bar (256GB SSD). The former can take up to about a minute to boot up from a cold start, while the latter is available for use in seconds. Likewise, there are usually lags in starting up some large apps — Microsoft Excel, for example — on the iMac, while the apps open instantaneously on the MacBook Pro. The result? I’m up and running faster, with fewer of the pauses and delays I see on a powerful iMac.

SSDs can provide productivity improvements for most Mac users, simply because of the near-instantaneous access to storage.

Check out the SSD page to find out how your existing Mac can be upgraded to the speed and reliability of SSD!


  • As much as I agree with the concepts of over-provisioning and garbage collection, the simple facts (and easily verifiable) is that TRIM works WITH OWC SSDs, not against them. A few bucks spent on TRIM Enabler or equivalent is money well invested, IMO. TRIM exists for a reason, as does garbage collection. They are not the same thing.

    Get your OWC super-quick SSD _and_ make sure that TRIM is enabled on your system. That’s my story and I’m sticking to it. We’ve a number of OWC-equipped systems in the house and all of them have TRIM Enabler.

  • Thank you for a thoroughbred understanding and explanation – I could now describe this to anyone else as you have lifted my learning and with such immediacy…
    (Ex IBM Agent/proprietor systems integration salesperson – installed much of the city of London financial institutions systems so I do not say this lightly)

  • i just wanted to say that I appreciate the articles that OWC has been making available.

  • OWC offers “Pro 6G” and another that does not have “Pro 6G” in the title.

    In plain English, what is the difference?

  • OWC 2TB SSD $800 (x 2 = 4TB) = $1600 ($0.40/GB)
    Very Fast 4TB HDD ~$100 ($0.025/GB)

    OWC 40TB SSD $28,000 ($0.70/GB)
    40TB HDD data RAID ~$1600 ( $0.04/GB)

    Yes, SSDs are way faster, but there’s still the critical consideration of ‘fast enough’/$$$.

    Pretty sure HDDs are, and will be, demonstrably cheaper and entirely suitable for even video for quite a long time to come; currently a 16-18x cost increase is still hard to swallow to store *all* your data.

    SSDs for boot and everyday data? No question. Spend the money. But don’t panic about getting all your music, movies, and archive photos/projects on SSD just yet. A single good HDD can easily deliver 170MB/s+ vs ~500MB/s Real World SSD; stripe a couple or more into a RAID, and you’re destroying an SSD of comparable size/cost.

    That said, if you’ve got the hardware to host it (c.f.: 2008-2012 Mac Pro), a pile of on-sale, small SSDs striped into a huge RAID 0 (with appropriate HDD backups) can make for a really fun daily driver.

    My 2008 Mac Pro using a RocketRAID 840a has a 4x SSD RAID delivering over 1480MB/s *sustained* read, using 4 of 16 available channels. The same card hosting 4x HDD RAID 0 delivers ~760MB/s sustained for a fraction of the cost and four times larger in size.

    Until both Apple and third parties deliver flexible, expandable, affordable(?!) host enclosures taking full advantage of Thunderbolt 3 and *true* PCIe interfaces for use with standard and top-end M.2 NVMe drives, we Mac owners are going to pay through the nose for lesser speeds and capacities than we should be.

  • You didn’t discuss SSD’s limited number of Write cycles. This case of flash ram wearing out after x million writes has kept me using HDDs. Comment?

    • Cause that’s not a myth. And they still last longer than HDDs. No heads to fail either.

    • I have been using Macs with SSDs for several years, and I have never had an SSD wear out. Speed was maintained throughout years of use.

    • Russ, you should be more worried about your HDDs crashing than you should be about exceeding the erase/write cycles on any given FLASH memory chip. I have a Mid-2010 17″ MacBook Pro that shipped with an SSD and I am still, to this day, using that same SSD. In the meantime, I’ve replaced any number of HDDs in other machines around it.

      That said, *always* have a backup — I just use Time Machine, built into macOS. Sometimes things go wrong unexpectedly and, if that doesn’t get you, all of your hardware *will* eventually someday fail — HDD or SSD. That said, while erase/write cycles are indeed a thing as it relates to FLASH memory technology, it’s quite safe to say that a modern SSD will by far outlast your HDD(s). Just stay away from the super-cheap no-name brands; “you get what you pay for” is still very true!