What do you do with a drunken hard drive?

What is RAID 0, 1, 5, & 10?

I was sitting outside enjoying a pleasant late summer afternoon when I got to musing about the pile of old disk drives I have sitting in a box. Surely something that 'valuable' could be put to good use. Of course value is in the eye of the beholder. When I bought them, or more likely the computer they came in, they were serious equipment. Okay, not serious serious, but more than adequate for my needs.

I've been thinking for awhile that there ought to be some way to combine them all into one giant storage device and since there's so many of them, I ought to build in some kind of security, like a RAID system. Never mind that the mix of sizes I have probably couldn't be configured in any kind  of RAID configuration. The biggest one is probably bigger than the sum of all the rest.

So then I try to remember how a RAID system works. I remember there is a system where if you have three or more disks, you can arrange the data so that if any one disk fails, you can rebuild the data from the remaining drives. You can do it with two disks but two disks doesn't require any mathematical magic, you just copy one to the other. Hence the video up top.

XOR is the answer. Here is an example I came up with for how it works.

We have five disks, each one can store one number (they are very small disks). The way this works is you XOR the data from the first four disks and store the result on the fifth disk (yellow). Now, suppose the third disk dies and you want to recover the missing data. You simply XOR the data on the remaining four disks and write the result (pink) onto the replacement disk. You will notice that the XOR sum of the data on the remaining four disks is the same as the data was on the now missing disk.

In order to rebuild the data on the new disk, you are going to have to read all of the data from the remaining four disks. If those are big disks, like in the terabyte range, that's going to take a while. The SATA disk interface can transfer data in the range of 100's of megabytes a second, so a terabyte is going to take on the order of a thousand seconds. Reading four disks with an actual computer system is liable to take hours, just so you know what you are getting into.

Okay, back to the original 'problem'. 

My hard disk collection

I bought the big Western Digital disk when I had hopes of consolidating all of our family's photos, but kids these days, they don't care, and evidently I don't really care as I haven't spent much time on it. I gave up trying to use Western Digital's fancy backup system and resorted to using an external hard disk adapter.

Unitek USB 3.0 to IDE and SATA Converter $35

Of course now-a-days you can buy a 2 TB USB stick for $40:

2TB USB Flash Drive $40

Problem with USB thumb drives is they are small and easily misplaced. Fortunately this one has a key ring so you can chain it to a boat anchor like they do the restroom keys at roadhouse restaurants.

So for a couple hundred bucks I could stuff all my old hard drives in shoe box with a bunch of USB adapters, a USB hub and a power strip and I could have my very own giant data storage complex. But then I would need to organize my pitiful collection of files that probably wouldn't add up to 100 GB much less a terabyte, so I'm probably not going to do that. 

I could try and sell them, but used hard drives are worth almost nothing, and certainly not worth the time and trouble to pack them up and take them to the post office. Shipping them out one at a time I would need $50 each to make it worth my while and I don't think anyone is going to pay that kind of money for these antiques.

I can't just throw these old drives away, it just goes against everything I believe, so it looks like they are just going back in their box and back on the shelf. Maybe one of these days something will change and they will once again become valuable.