September 13, 2005

Carbon Copy Cloner to the rescue.. again

Just when I thought I'd said all the good things I could say about Alsoft's DiskWarrior, I ran across a problem it couldn't fix. After a dozen emails and a phone call or two with their tech support, I decided to reformat the drive. Maybe I should back up a bit.

Everything was working fine, but trying to verify/repair my main boot disk always resulted in an "invalid extent entry" error. I'm not sure exactly what that means, but it's something like "we lost track of one of your files and can't fix it." Among other things, Alsoft had me run Apple's Hardware Test CD which failed first on my Firewire bus. A little googling revealed that my Firewire/USB PCI card always causes a failure on this test, so I removed it. Then the test started failing on my computer's memory. It seems I may have had a bad RAM SIMM in my machine, though Apple's startup memory tests never said boo. Rember thought all was well too, but after numerous AHTCD runs I could only conclude that that the middle SIMM was bad. Other World Computing offered to replace it without a moment's hesitation. Lately I've been pondering buying a cheap PC for my next computer. I mean, they're SO CHEAP. But, like with shoes, you get what you pay for. Apple computer may be relatively expensive, but that's because they're of relatively better quality.

After much debugging work with Alsoft, their tech agreed that even if DiskWarrior can get the directory repaired, I might not want to use that repaired directory. Memory problems can reek havoc on a file system, and on DiskWarrior, so it's on to plan B.

Plan B is to copy everything off of the hard drive, reformat it, install OS X 10.4 from scratch (I've been upgrading since around 10.2), then reinstall all of my files and programs. Hardly a picnic.

Plan C, however, is to use the wonderful Carbon Copy Cloner to copy my whole startup disk to a disk image on another drive. Then reformat the drive and copy everything back. If any files were hosed beyond recognition, they simply wouldn't make the transfer and I would deal with that later. I wasn't sure this was going to work, but after copying everything to the disk image and checking it's integrity, things were looking fine. Besides, my home directory is backed up nightly so at worst I would have to reinstall the OS and all my apps (plan B above).

After a bit of hesitation over the "OK" button I reformatted the drive and started copying all 600,000 files back, again with Carbon Copy Cloner. Checked the disk, repaired permissions, rebooted and... it worked! I'd heard CCC could pull such things off but I wasn't entirely sure it would work. Everything seemed to be working fine, the directory is in good shape, and it's basically like the machine never missed a beat. I didn't get the potential speed gain that a fresh install might have yielded, but I also saved a day of popping CD-ROMs in the drive.

One potential boneheaded move, which I've confronted before, is that nightly home directory backup. Sure, that's great if I delete something by accident, but since there's only one backup I have to catch the problem within 24 hours. While I slept last night, having just copied everything back to my main disk, this backup occurred. My safety net was overwritten with the supposedly restored data. I guess I need more space to have 7 rotating nightly backups?

Having a small business that depends on digital data has made me confront the realities of backups. I have a pretty decent system in place, but it's still not foolproof (or Randy-proof) nor is it 100% robust. Storage space is cheap these days, but when one copy of your work data consists of about 200GB, and that's just 14 months of work, it starts to look expensive again.

Posted at September 13, 2005 10:17 AM, Categories: Computing
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