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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)?

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

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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.

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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

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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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