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The other day I had what I thought was a great idea - I could buy up a bunch of cheap USB 2.0 drives and fill up the spaces in my 7-port USB hub for a super-fast RAID device! But in the light of day it isn't looking so good. I think that this would give me faster read times at least, but how would write times fare? Which RAID level would be best suited for this purpose? (I am trying to optimize for speed, any data doesn't need to be particularly safe.)

If this is a "good idea", or at least not completely foolhardy, how would I go about setting this up? I run Ubuntu 12.10 and Windows 8.

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That would be incredibly slow. First, cheap USB 2.0 drives are slow to begin with. Second, every operation would require a large number of individual drive operations that would be fighting for the same USB bus. It's a horrible idea. –  David Schwartz Dec 25 '12 at 23:48
    
I've heard of someone doing it with floppy drives back in the day. Linux is probably a better bet here, with the built in softraid option I suspect. –  Journeyman Geek Dec 26 '12 at 2:11
    
Yes, that's what I was thinking. too. –  WindowsEscapist Dec 26 '12 at 2:22
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You could use a USB 3.0 hub/devices. However, keep in mind that the failure rate for flash drives (especially cheap ones) is probably a hell of a lot higher than an actual internal drive, so you probably don't want to use RAID-0. –  Bigbio2002 Jan 3 '13 at 15:27
    
I think I'll end up mounting it on /tmp to if it fails it won't be that important (or if it is, serves me right for putting important stuff in volatile storage!). Sadly, I don't have USB 3 (that would fix a lot). –  WindowsEscapist Jan 3 '13 at 15:37

3 Answers 3

I would not suggest using a USB 2.0 raid method as the transfer rate between that and an internal mounted hard drive (SATA or SAS) is significantly slower. Combined with the fact that you are using a USB HUB, it would make the transfer rate even slower thus defeating the purpose of a RAID setup.

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Building a raid out of a bunch of cheap usb thumb drives is a great idea. A 'must read' on this topic can be found here: http://analogbit.com/node/4

To summarize, up to six USB flash drives are needed to saturate usb bandwidth in most of the use cases. Lots of USB flash drive with low write speed are actually doing wear leveling internally (ex: Sandisk Cruzer Blade 4GB stuck at 4MB/s for this purpose). With only one flash drive, write speed is about 4 to 10 MB/s. With six flash drives in RAID 0, the write speed is as high as an external hard disk: no tradeoff is made between data safety versus write speed performance with that kind of setup.

About the use cases:

  • cheap storage possible
  • low power consumption
  • low heat
  • noiseless operation
  • no data safety vs performance tradeoff
  • size can be dynamically expanded

PS: I personally use a RAID0 made of seven Sandisk Cruzer Blade 32GB and a D-Link HUB H7 plugged on a OpenWrt router that runs 24/7. Total cost lower than a 256GB SSD and a 2.5" external HDD enclosure.

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Well, it looks like the limitations of a single USB 2.0 bus would cripple this idea. For some speed gain, I could use two flash drives per bus and use multiple buses (there are two on my laptop) for a total of 70 MB/s (Wikipedia says maximum throughput per bus is 35 MB/s, and each flash drive gives me roughly 20MB/s). However, this isn't that much - it looks like it was more feasible back in the days of floppy drives.

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