External HDD mirroring using USB Interface

Question

Has anyone out there explored the possibility of mirroring two external HDDs (identical ones) through the USB interface ? If so, I would like to know how it can be achieved.
When I say mirroring, I mean that a single write operation actually duplicates the information on two separate external disks simultaneously. Much like the professional RAID mirroring on more expensive solutions. I am looking at a very inexpensive way of having redundancy built in for safeguarding my data. Perhaps some app out there can do this for me ? Or perhaps this may be a good idea for a brand new App ? Compromise on speed may be an issue, but it would be great value for money.

Answer 1

That is actually a classic backup solution using time machine, where both boot drive as well as EHD is being backed up incrementally in a format which is native to OS Mavericks. Such a backup can only be used to "Restore" the files back onto the source machine. Excellent for normal backup operations.
However, what I have in mind is two sets of EHDs (external HDD) formatted to FAT or maybe the NTFS, where the files are kept in a standard format and can be read on ANY machine whether OS X or Windows.
On a proper mirrored system, both HDDs appear to be one only, and the filesystem also appear to be one. So when we handle a file from the mirrored system, the cloning on the two HDD is done transparently without the user getting to know of it. Failure of one HDD will not result in loss of data since that would be available on the other HDD, and when the faulty HDD is replaced, the data gets replicated again from the good HDD. Such a mirrored system is very expensive and not affordable by ordinary mortals like most of us.
So, to get around the expense part of the whole thing, now that we have fast USB3 interfaces, we can possible use 2 x cheap EHDs hooked onto two separate USB 3 ports, and use them as a mirrored set. It is understandable that since the computer cannot access two USB ports simultaneously, there will be some trade-off to the speed of handling the two EHDs, but, that is acceptable. At least we have two identical sets of data available, which can be used in an emergency on any other system. Should one EHD crash, we can always extract all data from the second one.
I am not sure if such an arrangement is possible using the existing functionality of the OS X, and so someone may need to whip up an app or a script for doing this. Alternately, some really clever geek could come up with some remarkable solution/work-around. Looking forward for some bright spark from somewhere.