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I am trying to contemplate how stupid an idea this would be...

I was inspired by some foolish fellow, who soon after the release of Mac OS X 10.0 took 5 USB floppy drives, plugged them into his iMac, and set up a RAID5 array on them.

Floppy RAID array.

But then I got thinking. In the office I am sitting next to a stack of 1 GB USB drives that are being given away to customers.

If I snagged say 5 or 10 of them, plugged 4 into a USB hub, duct taped them in place (You knew duct tape would come into this, once I started talking about floppy RAID arrays, right?), and set them up as a RAID5 array, how ridiculous would that be?

Ought to work, and be workable.

Now if I could find a stack of say 4GB keys and do that, a 12GB RAID5 array might be cool.

I am thinking that performance might not be too bad.

But then again, I could do a RAID 10 array for redundancy and performance I suppose.

Edit: As a side note, I think I would still stick with all the USB memory sticks on one hub, because then I can use duct tape to hold it all together.

I feel that the real value of duct tape, outweighs the perceived value of performance.

It's like lipstick on a cat. It seems like a good idea at the time, but eventually you realize that duct tape would have been a better choice.

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I've had the same thought. Never tried it though. On Linux... hmm. IIRC, USB scan typically comes after fstab processing so you may need to add a custom mount line later on to mount the RAID. It's crazy enough it just might work! –  sysadmin1138 May 20 '09 at 2:35

7 Answers 7

up vote 10 down vote accepted

I did this a while back. The machine runs Gentoo on a RAID-5 array of 9x2GB USB drives.

As the above posters noted, it's best to spread the I/O across various interfaces. That's why I have 3 drives connected to the on-board ports, 3 drives connected to a PCI USB card, and 3 drives connected to a PCI-E USB card. No hubs. Performance is really quite good!

You mention OSX above, but in case you plan to run Linux on the array: I had experimented with using XFS, to try and take advantage of its aggressive caching feature and the ability to match the RAID chunk size to the fs block size, but in the end I just went with EXT3. Read performance is of course very fast, and with the spread I/O, write speed feels like a mechanical drive. Also, make sure to use noatime,nodiratime in the fstab.

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I still think it is a pretty stupid idea. Probably will play with the notion just for the laughs. –  geoffc May 20 '09 at 13:28

In theory you could create a RAID volume out of connected USB drives, but the stupidity of the idea will come into play when you think about the following:

1) The fact that both drives are on the same USB chain may not give you much of a performance enhancement (if any) since the total bandwidth available on USB is not enough to satisfy multiple simultaneous drives reading/writing. It might actually be SLOWER on RAID.

2) If you ever need to move the drives to another computer.

I suppose if you really need a permanent fault tolerant volume on your computer it would beat having automated synchronization of your data. Still, how comfortable would you feel if some other component on your system failed and your volume gets stranded?

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If you want to do this, try to get your USB drives on separate buses - putting them all on the same bus, or on a hub, will slow down the performance of the array drastically.

Good luck with this!

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Top read speeds on USB drives are generally ~30MB/s (see http://arstechnica.com/hardware/news/2009/05/usb-flash-drive-roundup.ars), and USB is a terribly slow interface as it is -- I'll say this isn't going to be worth it, but I guess it would still be better than a floppy RAID..

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A little while back I played around with this on Windows 2003. At the time I was using the SQLIOStress utility to thrash test disks, and when I tried this it took about ten times as long as on the standard SATA disk in my (Precision 390) workstation then hung before completion and I had to restart Windows to clear it.

This is far from a definitive test, the keys I used were a couple of years old and newer keys may well be better. Also the keys were on the same USB bus, and as people have mentioned above this is a bad idea. Finally SQLIOStress generates unrealistically heavy disk loading except for really busy SQL Servers. Nevertheless if put me off USB disks big time.

In any case isn't there a (low) limit on the number of rewrites on USB keys. My impression is that although they're superficially similar to solid state disks the memory used in them is usually much cheaper and slower.

John Rennie

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The original Drobo IIRC was USB only so your idea is not "crazy" from the standpoint that a company actually built a product around it.

However, USB is just way too slow and does not have enough bandwidth to properly service multiple drives with decent IO. Personally, I would not do it unless it is for cheap archival.

Another thing to keep in mind is that power consumed by many low capacity drives is going to be higher than fewer high capacity devices.

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I am currently in the middle of creating a raid 5, 4 x 320G usb2.0 system, using an hp mini netbook and ubuntu. For all the people reading/replying to this posting, will this be a long term solution for mp3's, pictures, docs, etc... ? I am hoping I will have this low power (about 36W-40W power consumption) raid 5 solution for years.

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The 320 GB's, are they 7200 or 5400 RPM drives? Are you using a single USB chain or multiple USB channels? –  geoffc Jun 1 '09 at 17:35
    
They are the cheap toshiba usb external 5400 rpm drives w/ 32mb cache ($50 each at fry's). On further research, I am thinking about instead using raid 10, 2 of the drives on one usb hub and their mirror counterparts on the other usb hub. Each usb hub will be connected to a ups, and of course the netbook will shutdown properly if it loses power. Still the lower power/fanless operation will allow the whole system to be on the bookshelf, hidden and noise-free. –  Dave Jun 1 '09 at 19:48
    
The netbook has 2 independent usb ports/channels, 1 port for the main images and the other port for the mirror images. Can this be considered a long term solution for data? –  Dave Jun 2 '09 at 14:36

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