The cruellest cut

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Published:  January 13, 2010
Desktop
The cruellest cut

Many of us have felt it. It’s physical more than emotional. Your stomach seems to squeeze in on itself, causing your whole pelvic region to tense up; your throat constricts and it feels like invisible hands are reaching up from your chest to pull it downwards. No, this is not the first terrifying drop of a rollercoaster we’re talking about, but the moment you realise you’ve lost some data.

Of course, you have an iron clad, twice-redundant back-up regime, so you don’t have to worry, right? Just remember, it’s just as likely that the day you were working on that huge project and didn’t get time to back up the night before will be the day your server starts pouring smoke, your computer has a head crash or you mistakenly drag the whole WIP folder into the trash and empty it before you realise what you’ve done. Yikes!

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First of all take a deep breath, and remember The Hitchhiker’s Guide to the Galaxy’s advice – ‘don’t panic’. Most of us with any IT knowledge know just because you delete something doesn’t mean it’s not there anymore, and the reason for this is thanks to hard drive technology. All disk-based media contain a little firmware straight out of the box that divides the entire disk up into tracks and sectors. Each sector on a mass market hard drive comprises a 512-byte ‘slice’. When you install an operating system it creates a catalogue or record of each sector and its contents, and as you save or create files the catalogue is altered so the read/write heads of the disk (like the stylus on a vinyl record player) know where the files you need are physically located on the platters’ surfaces. So when you delete a file it’s not removed from the sectors in question, they’re just marked as available.

The above short lesson in hard drive technology is the reason why the next step is so critical. If you go installing data retrieval programs, resaving old documents and panicking as you create or delete more files to try and get the data back, there’s more chance you’ll overwrite the sectors that contain your lost data, sectors the computer now thinks it can reuse – and if it’s overwritten, it’s truly gone. So the next step is to make sure you keep the affected drive absolutely sacrosanct. If you can, boot up from another drive. Remove the affected drive and put it in another computer where it becomes a second drive. The reasoning is that you can now make a complete clone of the disk. Doing so is easy – there are a hundred free, cheap and full-featured disk cloning tools all over the web, and if you have IT smarts then you can do so using the command line in Windows or Terminal for Mac.

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This isn’t also just so that the original drive is safe, but because there’s more than one way to skin a cat. You may want to try a shareware utility first, before working your way up to a commercial data retrieval service (most jobs can be bought in at under $500), and for each attempt you’ll want a clean cloned copy of the disk, so make several – all you’ll have to lose is some disk space. If you have access to a studio or workplace server you’ll probably have room to do this, but clear it with your IT guys. If it’s just you and your stand-alone system, ask yourself how much your data is worth – a quick cost benefit analysis may come out in favour of getting a large removable hard drive, particularly as you’ll have a good back-up media so this doesn’t happen again. You need only install a stripped down system on it and reset the boot order in your computer’s BIOS settings, so it boots first and loads the affected drive on the desktop as if it were a removable disk.

The best way to be forearmed is to be forewarned, so understanding a little about how data loss and retrieval works is your first line of defence.

Hard drive crashes are devastating, but they’re not uncommon. Unlike a vinyl album stylus, the read/write head of a hard disk doesn’t touch the disk, but floats above it as if aquaplaning. If they connect you’ll hear a horrendous sound from your PC’s innards and end up with a scratch. If you’ve heard any of the sounds on this website, trouble’s afoot.

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While a hard disk is a well-contained, stable device, bumping or dropping one while it’s working can cause a ‘head crash’, which is why notebooks are more susceptible and many recent models have a reflexive accelerometer that draws the heads away from the disk if it senses the system falling or tilting.

Most data loss is the result of bad sectors on your disc. With each one taking up 512 bytes of space, there are over 488 million of them on a 250GB disk, so you’re unlikely to run into a lot of problems. If your disk is physically damaged (warped, bent or split) rather than just scratched then data retrieval becomes much harder, as the trick to reading it is to get it spinning again. Some say it’s impossible, but like all things the more money you have to spend the more outlandish the workaround.

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Once a disk with lost data is spinning, data retrieval equipment or software can make several ‘passes’, recreating the data in bad sectors one byte at a time and filling in the gaps to complete the picture. While that sounds hit and miss, remember that a text file containing only a single character measures in at only about 4k. Out of 4000 bytes, a few bad sectors of 512 bytes spread here and there can’t do too much damage.

In the case of laptop systems, don’t pick the machine up as soon as you’ve clicked ‘save’ or started moving a large file. While the disc is working, the heads are close to the disk platters, so any sudden movement could cause a dreaded crash. Take special notice of removable devices too. Any platter-based hard disk technology gets hot and needs adequate ventilation. A temperature increase of just 10 degrees in your external memory device will halve its lifespan, so be aware of how well-aired it is and whether air can get out as well as in – if vents are in the wrong place, hot air may simply be trapped inside.

And, for goodness sake, back-up.

Thanks to Xyber Computer Service Centre (xsyber.com.au), who provided technical information and advice for this story.

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