The Cruellest Cut

May 1st, 2009 Desktop, Tech, Tech Features

Feel like you’re only just staying ahead of your workload? How will you handle it when the loss of critical data holds you up for a few more days? Drew Turney braces himself for the worst.

Many of us have felt it. It’s physical more than emotional, your stomach seeming to squeeze in on itself, causing your whole pelvic region to tense up, your throat constricting and feeling like invisible hands are reaching up from your chest to pull it downwards. Not the first terrifying drop of a rollercoaster — we’re talking about the moment you realise you’ve lost data.

Of course, you have an iron clad, twice-redundant back-up regime so you don’t have to worry, right? It’s just as likely the day you were working on that huge project and didn’t get time to back up the night before will be the day the server starts pouring smoke, your PC 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.

Firstly, take The Hitch Hikers Guide to the Galaxy’s advice and don’t panic. Most of us with any IT knowledge know just because you delete something doesn’t mean it’s not there. The reason why 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) knows 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 which contain your lost data, sectors the computer now thinks it can reuse. If it’s overwritten, it’s truly gone.

The next step is to make sure you keep the affected drive absolutely sacrosanct. If you can, boot up from another drive. Take the affected drive out and put it in another computer where it’s a second drive. The reason is so you can take a complete clone of the disc. 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 you can do so using the command line in Windows or Terminal for Mac.

The reason isn’t just so the original drive is safe but because there’s more than one way to skin a cat. You might want to try a shareware utility first, then work your way up to a commercial data retrieval service (most jobs can be bought in at under $500). For each attempt you’ll want a clean cloned copy of the disc, so make several — all you’ll have to lose is some disc space.

If you have access to a studio or workplace server you’ll probably have room, but clear it with your IT guys. If it’s just you and your standalone system, ask yourself how much your data is worth — a quick cost benefit analysis might come out in favour of getting a large removable hard drive, particularly as you’ll have a good backup 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.

Help yourself

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 common. 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 PCs innards and end up with a scratch like those you can see in some of the images on these pages. If you’ve heard any of the sounds on this website (http://datacent.com/hard_drive_sounds.php), trouble’s afoot.

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’s over 488 million of them on a 250GB disc, so you’re unlikely to run into a lot of problems.

If your disc is physically damaged (warped, bent or split) rather than just scratched data retrieval is 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. It’s said the US National Security Agency puts a bullet through old disks when they retire…

Once a disc 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 4,000 bytes, a few bad sectors of 512 bytes spread here and there can’t do too much damage.

You might also be tempted to defragment often, but in the 100Mb disk drive days it was a lot more relevant. Unless you’re moving huge video or media files often, not much can throw your disk catalogue into disarray. It’s said defragging gets performance gains of less than 2 percent and if you have bad sectors, defragmenting will only increase your chances files are written to them and damaged.

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 ten 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 might simply be trapped inside.

And for God’s sake, back up.

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


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