USB drive RAID array

Solution 1:

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.

Solution 2:

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!

Solution 3:

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?

Solution 4:

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..

Solution 5:

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.