Just wondering, can read/write cycles on a Macbook's internal SSD be avoided by downloading files from the internet to an external hard drive?

I'm not sure how macOS handles this so I'm wondering:

  1. Does downloaded file content go directly to the external drive, or does it pass through a cache or similar buffer on the SSD first?
  2. Does the method of calling the download matter? For example, initiating download via Safari, via a download manager, via terminal?
  3. Aside from the problem slower speed of downloading resulting from the slower read/write rate of the external drive, would downloading to the external drive help in the lifecycle of the SSD or is this a pretty useless way of preserving it?

Thank you

  • With modern hardware, the speed of the target drive is NOT the limiting factor for download speeds, by far.
    – nohillside
    Commented Dec 2, 2021 at 5:52

1 Answer 1


Your questions:

  1. It goes directly to the folder specified in Safari's General preferences. Verified using FSMonitor.

  2. Yes, it will depend on the application being used. There is no common preference for Safari, a download manager, or wget.

  3. It is pretty useless way of preserving it. Most of the activity on the boot/system SSD is apps, preferences, system services - nearly everything uses that SSD and all day long.

For a while I had my ~/Downloads on an external SSD, but realised this was stupid as most downloads need to be copied (slower than moving) to /Applications or ~/Documents which are on my internal SSD.

My internal 512GB SSD is nearly 3 years old and still has 96% of its life remaining - measured via its SMART values. My external SSD (same age) has 99% remaining.

I hope that goes some way to persuading you not to over think the life of the SSD.

  • Excellent answer to a fairly broad and multiple question chained together. Well done. I wonder if you might add an answer here ecplaining how you measured use on the SSD on this post apple.stackexchange.com/questions/13884/… ( In the decade since asking that question I’m delighted at the durability and lifespan of Apple SSD. It’s truly been a non-issue for me)
    – bmike
    Commented Dec 2, 2021 at 9:28

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