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Hard Drives

7 minute read

Post-production environments require stable, large-capacity, high-performance storage. Playback response, file transfer times, transcoding, rendering, media access by multiple users (or not) are all affected by your choice of storage. But which choice is right for you? Let’s start with hard drives.

When referring to hardware, hard drives are more broadly classified as persistent storage. Persistent storage is where data (e.g. files) is created, written, read, then stored for later use after your computer shuts down.

Sometimes, hard drives are confused with memory. As in, “I need to back up my files! My computer’s running out of memory!” What’s the difference? With memory, or Random Access Memory (RAM), data is stored and referenced temporarily for rapid retrieval. Unless that data is written to a file in persistent storage, it won’t stick around after the host computer shuts down. So memory and hard drives, not the same thing.

Back to hard drives. Here are two types:

  1. 1
    HDD – Hard Disk Drives
  2. 2
    SSD – Solid State Drives

An Overview of HDD’s vs SSD’s

Hard Disk Drives consist of disks attached to a motorized spindle (the “hard disks”) working in concert with a magnetic head on an actuator arm. When the HDD is in use, the disks spin up (at thousands of RPM) while the actuator arm seeks a target position on the platter. Once reached, the magnetic head on the arm writes or reads data to the platter, repeating that motion until the operation is complete.

In Solid State Drives, mechanics are quite different. Instead of spinning platters and magnets, solid state chips are used for storage, while an advanced controller writes and reads data to those chips. In essence, the underlying tech used for RAM is now applied for persistent storage.

In general, SSDs are much more expensive, somewhat more durable, and a lot faster. HDDs are generally cheaper, but they can be slower and more prone to failure because of all of the fast-moving components.

Solid State Hard Drives are hybrids of HDD’s and SSD’s. A smaller capacity SSD and a larger HDD work with an operating system to provide fast access to a user’s most frequently used files. Eventually, the OS will have to use the much slower HDD for accessing files. Given the inconsistent performance of SSHD’s and their reliance on the operating system to function as intended, they’re not recommended for media drives, but make perfect boot drives.

Key Attributes

The one thing you know: you’ll need a drive with plenty of space (or capacity). If you’re comparison shopping, you’ll encounter even more information. What does it all mean? Does it really matter? Chances are, it will. Let’s demystify some of these terms:

Capacity – the amount of data a drive can store. Available in quantities of:

  • Gigabytes – 1 GB = 1000 Megabytes
  • Terabytes – 1 TB = 1000 Gigabytes
  • Petabytes – 1 PB = 1000 Terabytes

Sustained throughput – the amount of data that the hard drive can read or write continuously.

Interface – the physical connection of the drive to the host computer.

  • This is important because the interface can be a bottleneck for the data moving on and off of the drive, affecting sustained throughput.

RPM’s (HDD Only) – Revolutions Per Minute. This is how fast those platters spin in an HDD. More RPM’s mean faster media access.

Drive Cache or Buffer (HDD Only) – like RAM in a computer, an HDD has its own bit of memory to quickly read and store data. The greater the cache size, the more data can be stored there, which means more media access performance gains.

Sequential Reads and Writes (SSD Only) – the possible sustained throughput of an SSD for either of these disk operations.

Reliability & Drive Failure

A good indicator of drive reliability can be found easily: the manufacturer’s warranty. If the warranty is 3 years or more, that’s a good sign of their confidence in the product.

Unfortunately, drive failure isn’t a matter of if, but when. Most drives come with S.M.A.R.T support, Self-Monitoring, Analysis and Reporting Technology. With SMART support, a drive may notify you of impending failure before it occurs. Many times, that doesn’t happen, and SMART errors aren’t the whole story.

Sustained Throughput (Deeper Dive?)

Think of water as it travels through a pipe. The bigger the pipe, the more water can travel through it. That’s the idea behind sustained throughput. The faster your hard drive is, the more data you can read or write per second.

Between large media files and demanding timelines, choosing storage that can handle a high volume of sustained throughput at any moment is another piece to maintaining momentum throughout your project and delivering on time.

It’s also vital to understand your entire data pipeline to make sure that there are no bottlenecks. You might have a huge pipe that can handle a ton of water, but if you screw a tiny hose onto the end, then the water won’t come out very fast. So, you might have a super-fast SSD, but if you connect it to your computer via USB-2 (the old USB standard), then your data is going to move very slowly.

Here’s a quick key on bitrates:

  • Mb/s = 1 Megabit per second
  • MB/s = 1 Megabyte per second = 8 Mb/s = 8 (bits makes a byte) * 1 Mb/s
  • Gb/s = 1 Gigabit per second = 1000 Mb/s

Interfaces

A hard drive’s interface is the physical connection to the host computer, and an indicator of possible sustained throughput during its operation.

Here are some common interfaces and their maximum supported throughput:

Serial ATA or SATA (Internal or External)

  1. 1
    III – Up to 6 Gb/s
  2. 2
    II – Up to 3 Gb/s
  3. 3
    I – Up to 1.5 Gb/s

Thunderbolt

  1. 1
    3 – Up to 40 Gb/s, bi-directionally
  2. 2
    2 – Up to 10 Gb/s, bi-directionally
  3. 3
    1 – Up to 10 Gb/s, bi-directionally

Ethernet (often labeled in Gbps or Mbps)

  1. 1
    10 Gbps
  2. 2
    1 Gbps
  3. 3
    100 Mbps

USB

  1. 1
    3.1 Gen. 2 – Up to 10 Gb/s
  2. 2
    3.1 Gen. 1 – Up to 5 Gb/s
  3. 3
    3.0 – Up to 5 Gb/s
  4. 4
    2 – Up to 480 Mb/s
  5. 5
    1.1 – Up to 12 Mb/s

Firewire

  1. 1
    800 – 800 Mb/s, bi-directionally
  2. 2
    400 – 400 Mb/s, bi-directionally

RPM’s (HDD Only)

Another factor to HDD performance is the RPM’s, or Revolutions Per Minute, of the platter. The higher the RPM count, the faster your drive can access data. How fast do you need, though?

Anything less than 7200 RPMs is probably unsuitable for high-performance media drive use. If you’re looking for a low-cost backup, archive, or general storage solution, then a slower hard drive may be fine, but (generally) the higher the RPMs, the faster the drive will be.

It’s not just the RPM’s, though.

Drive Cache or Buffer (HDD Only)

A drive cache, or drive buffer, is a bit of memory bundled with a HDD. If the HDD has a substantial cache size, more data can be written, read, and accessed from this high-speed storage point instead of its platters. Remember, an HDD is a series of moving parts working together as fast they can. But the choreography of platters, arms, and magnetic heads won’t outpace the sheer performance of solid state chips.

But what if the whole drive was a solid state chip?

Sequential Reads and Writes (SSD Only)

Since SSD’s contain solid state chips with no moving parts, forget what you know about RPM’s and cache size. What you will see are listings for these details:

  • Sequential Reads – Compressible & Incompressible Data
  • Sequential Writes – Compressible & Incompressible Data

Those are followed by a number of data units calculated per second (e.g. 500 MB/s, or Megabytes per second). This is an indicator of the possible sustained throughput during its operation. Remember: 1 Megabyte per second = 1 Megabit per second multiplied by 8.

Let’s put this all together.

Hard Drives and Video Playback

Let’s say you’re working in Avid Media Composer, and you’re working with footage transcoded to the DNxHD 145 codec. With DNxHD, the number is the bitrate of the media, or the size of the water moving through the pipe, measured in megabits (not bytes) per second. So a file encoded in “DNxHD 145” means 145 megabits per second of throughput will need to travel between the drive and its host computer.

Once that clip’s inserted in your timeline, it becomes one stream of video occupying around 145 megabits on playback. Insert another clip on top of your existing clip, and one stream becomes two at around 290 megabits per second of throughput How many streams can a hard drive handle?

Let’s go back to that SSD rated at 500 megabytes (not bits) per second of throughput. Since a DNxHD 145 file’s bitrate is 145 megabits per second, we’ll convert the SSD’s rated throughput of megabytes per second (MB/s) to megabits per second (Mb/s):

Megabytes per second * 8 = 8 Megabits per second

500 MB/s * 8 = 4,000 Mb/s

So if one stream of DNxHD is 145 megabits per second, and the SSD is rated at 500 megabytes per second, we can convert the codec’s bitrate to determine how many streams of video could be played simultaneously on a timeline from this drive.

(4,000 Megabits per second) / (145 Megabits per second) = 27 streams of video

On the other hand, if your files are 8K Redcode Raw at 1,216 Mb/s, that super-fast SSD will only be able to handle 3 streams, max.

Of course, all of this is assuming the drive is connected to a host computer with an interface that allows the maximum amount of throughput. But what if someone decided to install that SSD in a USB 2 enclosure? Or what if it’s a part of shared storage appliance connected over Ethernet at 1 gigabit per second? All of these are potential bottlenecks to your desired sustained throughput.

This is why many editors love to cut using low-bitrate proxies like DNxHD 145—because the data speeds are very manageable without high-performance hard drives.

Choosing the Right Hard Drives

Again, postproduction requires stable, high-performance storage. Usually it comes down to budget, but SSD’s and premium HDD’s have become more and more affordable. Weighing out all factors and deciding on the right storage will save you time in the edit, and help you deliver on time.

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