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How does a hard drive compare to Flash memory working as a hard drive in terms of speed?

I recently purchased a 16GB USB 3.0 flash drive, and I'm considering using it as a mobile operating system. It would be nice to carry with me, but I'm worried about any performance impacts from running off a flash drive, and using it as the hard drive. What downsides can I expect to encounter, both at USB 3.0 speeds and USB 2.0 speeds (as not all computers have USB 3.0 yet)?

marked as duplicate by Dave M, Indrek, Nifle, MaQleod, slhck Oct 4 '12 at 18:49

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  • @DaveM - While speed is one factor, and based on the answers appears to be the most significant one, I was curious about anything on a flash drive impacting OS performance, not just read/write speed. – SaintWacko Oct 4 '12 at 20:56
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The problem is that flash-drives are quite limited in speed as compared to spinning hard-drives and SSDs. This is because by their nature, they are not meant for high-performance usage and so use simpler, more basic mechanisms than a comparable SSD or hard-drive (which is also why they are much cheaper).

You can (currently) expect typical read speeds <=20MBps and write speeds <=10MBps. This is usually going to be slow enough that unless you are just using it as a live-OS type of system for data-recovery and such (i.e., occasional, emergency usage), then it will be too frustrating for regular, every day usage.

What is worse, is that by running an OS from a flash-drive, the non-stop writes for logs and temporary files will really eat into the flash-drive’s lifespan. Don’t forget that flash-cells have a limited number of writes before they can no longer be written, and these constant writes will use them up too fast, even with wear-leveling because again, the writes and leveling used in inexpensive flash-drives is not as efficient as with SSDs (which use things like TRIM whereas flash-drives tend not to).

You could run an everyday OS from a flash-drive, but ones that are going to be fast enough will usually also be expensive enough that you may as well just get a cheap SSD and benefit from the enhanced wear-leveling as well.

  • I have seen special linux distributions (to lazy to find examples) that just boots from the USB and runs of a ram-disk. They only write to the USB occasionally (typically on shutdown) – Nifle Oct 4 '12 at 17:58
  • Oh, I was thinking about the read/write speed, but I forgot about the wear. Guess I'll probably end up just installing portable programs on it instead. – SaintWacko Oct 4 '12 at 18:30
  • @Nifle, good point. Somehow I assumed this question was about Windows (which can also use a RAM disk, like Bart’s PE, but I took the question to mean using the flash-drive as a drop-in replacement with a normal, non-live/static system). – Synetech Oct 4 '12 at 21:31
  • @SaintWacko, yup, that’s works great. In fact, flash-drives were what made portable programs really off a few years ago. (Personally I prefer portable because I like to know what changes are made to my system—actually I don’t want any changes to be made. I once dabbled with installers, but all of my programs have been portable ever since.) – Synetech Oct 4 '12 at 21:32
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With regard to the speed variances in drives, this article has some interesting information. Symantec USB testing

  • Do you know of any tests with USB 3.0 (where flash drives can actually work faster than SATA-2 in theory) – Earlz Oct 4 '12 at 17:36
  • USB 3.0 can't work faster then SATA-2 – Ramhound Oct 4 '12 at 17:59
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There are no downsides to it apart from performance. And that too depends on the USB Drive you get. A 20 dollar 16GB vs a OCZ 40$ 16GB USB Drive show visible difference when running an OS. Also, it completely depends on the OS too. IF your running Linux, no sweat. If it's Windows, then consider getting a faster USB Drive. USB 3.0 certainly is a lot faster but you want to be able to use your OS everywhere and hence should stick with USB 2.0

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