Data Integrity a Posteriori

Posted by cwright on 2008.03.01 @ 20:03

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 Corrosive Liquids.  Wear Protective Equipment.Data integrity is a hot topic these days. With data volumes on the rise and hard drive half-lives falling, protecting data has become important in many different fields.

Conventionally, a storage medium will report its life expectancy in terms of MTBF, or Mean Time Between Failures. This is often measured in hours. However, it’s not always this simple. Usage patterns and environmental characteristics take a heavy toll on how long our storage devices last.

One fun experiment I unintentionally tried this afternoon helps provide one data point that goes above and beyond our classical MTBF estimate, and into the realm of – shall we say – aquatic endurance?

Several months ago, I purchased a SanDisk 1.0GB Cruzer Micro USB flash drive. I used this as spill-over when I took too many videos without flushing the data off of my camera while I was in Utah. Since I didn’t have a personal computer, and only had limited computer access, the best I could do was shuffle data between various solid-state devices. So this device has been filled to capacity a couple times, and has been completely erased a couple times, and has had various data-shuffling jobs in between for the past 9 months or so. Despite being dropped, being X-Rayed at SLC Airport, and being kept in pockets for long periods of time in various weather extremes, it has held up like a champ. I’ve not lost anything, nor have I had any problems shuffling data between my laptops and desktops, as well as other machines.

This experiment, however, was above and beyond the typical environmental exposure these devices normally take. Today, my little USB drive got to take a swim through our Frigidaire Washer and then through our Whirlpool Dryer. For what it’s worth, the Washer is a sideways one, so it uses less water. This might have been the show-stopper in disguise.

The reason this all happened is because I normally hold all of my belongings in my pockets. That’s what they’re there for, after all. Because I was shuffling data around last week, I must have left it in one of my pockets.

Upon finding myself nearly out of clothes for the week, I opted to do laundry. My work clothes were especially dirty (landscaping tends to get lots of dirt on your hands and clothes) so I opted to wash with the Heavy Wash Cycle, which takes about 25-30 minutes, to get my clothes all clean and ready for the coming work week. It was a fairly large load; several (4) pairs of jeans and many (5) shirts. No socks.

After washing, I like to get my clothes into the dryer as soon as possible to avoid the mildew smell. I’ve never had much faith in the “automatic” setting on dryers, so I put all the clothes in for 60 minutes. Since I had more than 2 pairs of jeans in there, I also extended the dryer time an additional 20 minutes once the first 60 expired because my jeans like to hold irrationally large quantities of water and are never dry after a mere 60 minutes of high heat. After this duration, I removed my clothes, and discovered my flash drive sitting comfortably on the bottom of the dryer cylinder. This, of course, made me a bit downhearted. Cellphones can’t endure this kind of rough treatment. Palm Pilots can’t either. I wouldn’t dare try it on a camera, CD player, or Social Security Card either. From past experience, things were looking grim for this little data carrier.

As with any storage medium loss, the first thoughts through my head were “What did I put on that device that isn’t backed up somewhere else?” Thankfully, I couldn’t remember anything. This was in part because I haven’t explored it much in a long time, making me likely to forget. It’s always easier to lose data if you can’t remember what it was anyway.

Deciding to test it out and see what I could salvage, I decided to plug it into my laptop and see what would happen. I was partially expecting it to cause my laptop to reboot; I’ve seen computers where shorting the USB +5V and Ground pins acts as a poor man’s reset switch. If that didn’t happen (I’ve also seen where my MacBook is engineered to be at least a little more resilient than that), I figured it’d leave some fun console messages, do nothing, or have tons of data errors.

Much to my surprise, the disk lit up when inserted. It also blinked a couple times, characteristic of OS auto-mounting. This was good so far. The mounted volume showed up on my desktop, and lo-and-behold, all the data was there, intact. Currently, I have about 450MB of data on it. Disk Utility didn’t find any File System problems, and inspection using Finder didn’t either. The pictures show up fine, the MP3’s sound fine, and all the source code is intact. Since JPEGs and MP3s will be essentially useless if even a few bits are toasted, I find these to be handy metrics in the event of suspected data corruption.

So, when looking for devices that retain data above and beyond the call of normal duty, look no further. This little Cruzer took a licking, and has kept on ticking.