SSD vs HDD: Advantages of SSDs over hard drives

If you want to start a religious war, go on a forum and ask about an SSD vs HDD and why you should buy one over the other. I’m not quite sure why this is so controversial. But it is. Let’s look at the advantages SSDs have over hard drives, and when hard drives make more sense. I’ll also go into when I think this will no longer be true.

SSDs have numerous advantages over hard drives. They have faster seek times, faster read and write speeds, lower power consumption, less noise. they fail predictably, and are more reliable. The main disadvantage is cost, though even that is changing.

SSD vs HDD: Cost

Although hard drives hold the advantage in total capacity and cost per gigabyte, SSDs have considerable advantages in every other regard.

As of this writing, hard drives still have a cost advantage vs SSDs. I predicted in 2011 that sometime around mid or late 2020 or possibly in 2021, the balance would shift to SSDs. I may end up being off by a couple of years, but it’s still going to happen. The pioneering computer columnist Jerry Pournelle was fond of saying silicon is cheaper than iron. Eventually we’ll have the technology to use the cheaper element.

We’re seeing some signs of this. For example, it’s never been all that practical to sell a hard drive for much less than $50. You can find end-of-life or refurbished drives below that price point, but what you can get will vary from week to week. But the point of diminishing returns on SSDs is lower. Entry-level 120 GB SSDs are thriving at the $20 price point, and value-class 240 GB SSDs have taken the $30 price point. While that’s not a ton of storage, 120-240 GB is more than enough to hold an operating system and your most critical applications.

Cost per gigabyte

On a cost-per-gigabyte basis, at the time of this writing the cheapest non-refurbished 1 TB HDD I can find costs $42, and the cheapest non-refurbished 1 TB SSD I can find costs $80. And 1 TB is the sweet spot. At 1 TB, I pay 8 cents per GB. At 2 TB, I pay 11. And at 500 GB, I pay about 10 cents per GB.

With HDDs, the lowest cost per GB happens at a higher capacity. An 8 TB HDD costs $200, which is about 2.5 cents per GB.

If I end up being wrong about when hard drive and SSD prices reach parity, it’s because hard drive prices are dropping at a rate faster than I anticipated. I expected HDDs to sell for 3 cents per GB in 2021, and they’re below that price in early 2020. But some of those are using a dirty trick called SMR, which decreases cost, but with significant performance penalties.

Advantage: HDDs but with a caveat

The problem with the price advantage

The problem with saying hard drives are better because they’re cheaper is price isn’t the only factor. That’s kind of like saying Pentiums and Athlons are better than i5s because Pentium and Athlon CPUs are cheaper. The Pentium or Athlon is cheaper, but an i-series CPU is faster.

On paper, an i5- or i7-based PC with a 4 TB HDD is a more powerful computer than a Pentium with a 120 GB SSD. But the computer with the slower CPU paired with the cheap SSD is faster for basic computing tasks, because many tasks are storage-bound rather than CPU-bound.

SSD vs HDD: Capacity

Hard drives do have one other advantage over SSDs. I can get a 12 TB hard drive if I’m willing to pay $320-$400 for it. SSD capacity tops out at 4 TB, and you pay dearly for that capacity. A high-performance 4 TB SSD costs over $700, and a lower performance drive costs around $450.

If you store a lot of large files (video comes to mind), you might find 4 TB limiting. And you may not want to pay $450 for a 4 TB SSD when you can get a 4 TB HDD for around $110.

If you need a lot of capacity, your best bet is probably to get a 480GB or 1TB SSD to load your operating system and your most important software on, and pair it up with a 2 TB or 4 TB hard drive. That will be your best value play, balancing cost per gigabyte with performance. This is a common recommendation, but it assumes you need tons of capacity. That may or may not be accurate.

Advantage: HDDs, if you actually need the capacity

Do you need terabytes of capacity?

The people who need terabytes of capacity either do a lot of audio and/or video editing, or they have large collections of files. That could be a lot of PC games. It’s more likely to be a lot of video files. If you keep digital copies of all your favorite movies and TV shows, you can chew up a lot of space very quickly. And it’s certainly more convenient to pull up your favorite TV show on a computer than to hunt through a collection of hundreds of optical discs.

But an awful lot of people stream. It’s convenient and accessible.

I can see the argument that it’s more cost effective to put the $20 a month you’d spend on streaming services toward buying hard drives and DVDs or Blu-Rays and ripping them into digital format. And then it’s not a problem that you can’t stream Night Court or WKRP in Cincinnati because you can just get your own copies of whatever it is you want to watch and store them locally.

I’m not saying either approach is wrong. But if you use streaming services and cloud-based services, a $100 SSD may be all the storage you need and the lower cost per gigabyte of a hard drive may be irrelevant.

SSD vs HDD: Latency

Latency is the equivalent of the time it takes for a car to go 0 to 60. The reason people buy Corvettes instead of Honda Accords is usually that 0 to 60 speed. You don’t get a lot of opportunity to drive your Corvette 180 MPH.

Latency is the time it takes to find the file you want, or to find the blank spot on the disk to write your file. Hard drive latency has improved over the years, but today’s drives still have much higher latency than the first SSD I bought way back in 2009.

The typical seek time of a hard drive is around 12 ms today. That seems fast, but the seek time of a typical SSD is more along the lines of .12 ms. The SSD will find your file 100 times faster than a hard drive will. The seek time is so small that some people say SSDs don’t have a seek time. That’s not completely accurate, but SSD seek time is so small you typically won’t notice it.

Now, for reference, a Corvette goes 0 to 60 in 2.9 seconds. A Honda Accord goes 0-60 in 5.8 seconds. Twice as long. If a car enthusiast pays twice as much for a 2x increase, it’s reasonable for a computer enthusiast to pay 2-4 times as much for a 100x increase.

Advantage: SSDs

SSD vs HDD: Top speed

If you buy a SATA drive, both an HDD and an SSD will boast a top speed of 600 MB/second. But in both cases, that’s the theoretical speed of the bus, not the speed of the drive itself. Once the drive cache empties, you don’t get that kind of performance out of it.

But a value SSD can deliver sustained speeds of around 500 MB/second, and sustained write speeds of around 400 MB/second. A high-performance SATA SSD can deliver sustained speeds closer to the theoretical limit, around 550 MB/second reads and 500 MB/second writes.

Performance SSDs that connect directly to the PCIe bus can deliver 3.5 GB/second read speeds and 2.3 GB/second writes.

When performing random I/O, which is much more common, an SSD can’t saturate even the SATA bus. But during random writes, which is what they’re worst at, SSDs can still deliver throughput of over 150 MB per second. That’s along the lines of what an HDD delivers during sustained sequential reads. Hard drives aren’t especially good at random I/O either. They slow down to a couple of megabytes per second during random writes.

Let’s look at this another way. An i7-9700 is 2.5 times faster than a Pentium G5400. Enthusiasts gladly pay five times as much. Why do the same enthusiasts complain about paying four times as much for an SSD that delivers four times as much performance?

Advantage: SSD

Will you notice the speed difference?

Whether you’ll notice the speed difference is a fair question. With an SSD, your apps will load more quickly, and in a low-memory situation, both an SSD and an HDD can thrash, but the SSD won’t thrash as long. I notice the difference with an SSD more than I notice a faster CPU, so I’ve always been willing to allocate more of my computing budget to SSDs than to fast CPUs, even though CPUs always get the glory.

Random I/O and SSDs

The knock on SSDs early on was in regards to random I/O, particularly writes. But these problems date to 2008-2009 or so, and affected only select entry-level drives. Those poor performing controllers have been off the market for years now. But today, the cheapest hard drives have terrible random-write performance, so now the shoe is on the other foot.

Modern SSDs do worse at random writes than they do at anything else, but good hard drives aren’t good at random writes either. Bad SMR hard drives are terrible at random writes. And it’s when they’re both at their worst that you notice the difference the most. When both are at their best, an SSD is about four times as fast. When both an SSD and a good hard drive are at their worst, the SSD is about 60 times faster. An SSD at its worst is about 120 times faster than an SMR hard drive at its worst. SMR drives are cheaper, but not 120 times cheaper.

SSD vs HDD: Reliability

The biggest criticism of SSDs is that you can write to the cells a limited number of times before they wear out and fail. But the mechanical parts of a hard drive have a finite life expectancy too, and it’s hard to measure.

SSDs can move cells around to level out the wear, kind of like rotating the tires on your car. As a result of this, SSDs can easily last 10 years or more under regular use. I have 120 GB SSDs that I bought in the early 2010s that still work fine, so I have no reason to doubt the 10 year life expectancy. You can write a petabyte of data to an SSD and not kill it.

Hard drives can last 5-10 years too. I haven’t bought a new hard drive in about 15 years, so I don’t have recent experience in that regard. I can tell you that I’ve bought a few used computers over the last decade or so, some of them 10 years old, and they had working hard drives in them. Of course I was buying the survivors, so I can’t say with any authority how frequently this happens. The general advice I always heard when I would buy hard drives was 3-5 years, and that’s what I still hear today.

But I can tell you that SSDs can warn you when they’re nearing the end of their life expectancy, and if you load the manufacturer’s software on them, you’ll get a definite end of life date. I replaced my 40 GB SSD when it had about three months of life expectancy left in it.

Your personal experience will color your view on this one, but I have to give the edge to SSDs on this one.

Advantage: SSD

SSD vs HDD: Power consumption

A typical SSD consumes less than half as much power as a typical HDD. This means higher battery life in a laptop, and it means lower power bills when your computer is plugged in. Neither of them use the kind of power your CPU does, and in the home, this won’t be a deciding factor. In a datacenter, that may be enough reason to favor SSDs. Of course, the performance benefits are nice too.

SSDs have a reputation for being power hogs, but that’s due to a test that Tom’s Hardware Guide carried out more than a decade ago. Their test caused their SSD-equipped laptop to do more work than the equivalent HDD-equipped laptop. In a fair test where both computers carry out the same workload, the SSD-equipped computer wins.

Advantage: SSD

SSD vs HDD: Noise

I didn’t mind loud hard drives when they were all we had. But SSDs are silent. When I fire up a vintage computer today, especially one of my old computers with a performance SCSI drive in it, I mind the noise a lot more.

Modern HDDs aren’t super loud, but the silence of an SSD is nice. And considering I sat directly in a datacenter for about four years of my career and I think I have hearing loss from the experience, I can definitely appreciate their value there. If you’re careful how you do it, you can build a dead-silent PC if you use an SSD, an external power supply and a low-power CPU that can get by with passive cooling. I don’t go that far but it’s nice to have the option.

Advantage: SSD

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One thought on “SSD vs HDD: Advantages of SSDs over hard drives

  • February 13, 2020 at 1:41 pm

    It’s not quite true that SSDs top out at 4TB. Only the ones you can afford. Larger SSDs exist for data center use, but if you have to ask how much a 15TB SSD costs you can’t afford it. Data centers are willing to pay a premium for more capacity; on their scale the cost of real estate to house servers is a significant consideration.

    If you actually need enough storage to need an HDD, you should also think seriously about setting up a NAS rather than installing the hard drives on your computer. The NAS brings a big advantage: you can easily use file systems that can recover from the loss of a drive, something that is difficult to do on Windows or Mac desktop systems. (Linux can easily handle it.) You can also stick the NAS in a basement or closet to get away from the noise.

    If you have been a computer enthusiast for a while you can probably set up a NAS at little or no cost other than the drives. Use the 5 year old PC that you retired in favor of your latest one; you want one with a nice big tower case so you will have room for lots of drives, and an older one is better for this application because it will have more 3.5 inch bays. Install a free NAS-centric OS such as FreeNAS or OpenMediaVault. If there is anywhere appropriate in your case to mount it, add a cooling fan near the drives. If you go with FreeNAS you may have to install more RAM; the ZFS file system is hungry for it.

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