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Archiving data: DVDs, flash drives, hard drives?

Posted 2013-10-14

Originally, I intended to write a story under the title "saying goodbye to the optical drive". But after a few minutes of research, it turns out that, in my particular case, the optical drive may be on its way out, but it hasn't quite left the premises yet, and not just because I may need to rip a DVD or CD once or twice a year. Let me tell you a tale of backups and storage management.

I think my first USB flash drive was 128 MB. (Yes, that's MB, not GB.) And my first CompactFlash card 16 MB. So when I got my PowerBook G4 back in 2003, being able to burn a whopping 4.5 GB to a DVD was huge.¹ Back in those days, there was no Time Machine, so I'd often burn important data to DVD to back it up. I also got in the habit of burning video files of stuff I may want to rewatch at some point to DVD, as well as other types of files that I want to keep but don't necessarily need to have on my internal drive. So over the last decade I amassed seven containers with about 20 burned DVDs (or CDs) each. So that's over half a terabyte worth of data.

Then, in 2007 we got Time Machine, which backs up your internal drives to an external one. So with backups out of the way, the question is: where do I archive data that I can't or don't want to keep on my computer's internal drive?

Burning DVDs

In theory, you can burn (write) data to a DVD a bit at a time. In practice, you burn an entire DVD at a time. So you first need to collect all the files that you want to burn, and then it takes about 30 minute for the actual writing and another 15 or so for the system to check whether all the files were written correctly. DVD-Rs and DVD+Rs are slightly different kinds of recordable DVDs, but I think all DVD burners support both types now. They hold about 4.5 GB¹ and can only be written once. There's also dual layer DVD+Rs that hold about 8.5 GB, but they are a good deal more expensive and the burning is a lot slower. There are also DVD-RWs, which you can erase and use again for something else, but they're notoriously unreliable.

So burning DVDs is pretty inconvenient—even before optical drives started to disappear from Apple's computers. These days, you have to buy a separate USB Superdrive (or third party external DVD drive) to read and write DVDs and CDs. However, there is a big upside: they're pretty cheap. If you buy them in bulk, you can get them for as little as 20 cents a piece. Speaking of bulk: a DVD weighs about 17 grams. That's not a lot, but I keep them in containers that hold about 20. Those end up weighing about half a kilo for about 100 GB of data.

If you want to stick with optical disks (discs, whatever) for your own use, then you may want to look at blu-ray. But especially in the Apple world, few people can read them.

External hard disks

Hard disks are everything DVDs aren't. You can just write data without thinking about it, erase, write something else, no problem. And they're fast. HDDs have been limited by the speed of the USB 2 bus for a long time now. I'm very interested to see how fast my latest 2.5" USB 3 drive performs once I get a computer with USB 3. External HDDs have also gotten pretty cheap: that 1 TB one cost me 60 euros.

External HDDs have two downsides. Because they're so big, that's a whole lot of eggs in one basket. And even though they're fast, it still takes hours to transfer all that data, making it hard to make extra copies. The fact that there's an extra box tethered to your laptop all that time doesn't help.

But at least the 2.5" models that get their power over USB are infinitely better than the 3.5" models that come with their own power brick. I had three of those, but in each case either the power brick or the enclosure failed after some years. The drives themselves are fine though, but now I need one of these to use them. Also, the 3.5" drives are more than half a kilo, while a bare 2.5" drive is only 100 grams, 170 grams in the USB enclosure.

Mac - Windows compatibility is also an issue. I formatted my first USB HDD with the FAT file system, which both MacOS and Windows can read and write. But then I accidentally switched the power off, which corrupted the FAT so that new files started to overwrite old ones, so I lost a lot of data without knowing it. So you really need the journaled HFS+ file system, but then you lose Windows compatibility. (And FAT can't handle files larger than 4 GB.)

USB flash drives and SD cards

A year ago, I was shopping for USB flash drives and SD cards, and I thought that it wouldn't be long before those would be so cheap that they're a good alternative for DVDs. But at about 50 cents a gigabyte, we're not there yet.

USB flash drives are even more convenient than external HDDs: they have no moving parts and they're tiny, so they're easy to carry and when connected, don't get in the way of using a laptop. They can be fast, but especially older ones may be slow. You can get 128 or even 256 GB flash drives now, but to avoid the eggs/basket issue, you can also get several smaller ones. Avoiding the biggest and the smallest available gives you the best price per gigabyte, but on the other hand different sizes can be convenient for different things. For instance, I may want to make a copy of my photo library that's 90 GB on a 128 GB drive. Four 32 GB drives wouldn't work so well for that.

USB flash drives are especially useful for exchanging data with other people, or even with devices such as TVs and audio systems. However, for most other uses I prefer SD cards, because they provide a more consistent experience than USB flash drives that come in all kinds of weird form factors. It's also easier to find out whether an SD card is fast or not so fast before you buy it. With USB flash drives I'm reluctant to reformat them as HFS+, because I'm not sure I can format them in a way that allows other systems to read them. With SD cards this is not an issue, I can simply reformat those as FAT in my camera. SD cards weigh almost nothing at less than 3 grams. Another nice little feature on SD cards is the write lock switch.


Let's compare the different options:

  $/€/TB  Weight/TB
DVD±R455 kg
2.5" HDD60170 g
3.5" HDD35310 g
USB flash370150 g
SD card52090 g

So burning data to DVD is still one of the cheapest options—but only if you buy DVD-Rs or DVD+Rs in spindles of at least 50. And then you have to figure out how to store them. I've already copied a lot of that data on DVDs to a USB HDD, but I was thinking about having the second copy² on SD cards and get rid of all those DVDs. But considering the price of half a terabyte worth of SD cards, that can wait.

¹ It's really hard to find out how much data fits on a recordable DVD, due to the multitude of definitions of the gigabyte, rounding at various stages, general sloppiness and the need to inflate numbers for marketing purposes. And then there's the file system overhead and a little extra overhead that Apple imposes. But it's not all that meaningful anyway, as you'll rarely be able to fill up a DVD exactly. So I'm using 4.5 GB as a nice, round number.

² Data doesn't exist until it exists in two places.

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