So I've been using a Time Capsule for some time now to back up my work MacBook Pro, and about 6 month ago I attached to it a 500GB Western Digital external USB hard disk to have Time Machine doing backups of the other Macs at home (I work from home). Worked like a charm and has always been for 6 month (apart from a problem with the latest 7.4.1 TC/Airport firmware update, but I'll leave that for another post).
Then, over last week-end, the backups started to take ages, and failed quite often (those on the Time Capsule's internal HDD were still running fine). I'd have to unplug the USB HDD, turn it off for a moment then plug it back in to have it recognised by the TC.
Hmm... So I disconnected it from the TC and plugged it directly to my MacBook Pro and ran Disk Utility on it, which reported, gasp,
May 25 14:30:59 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:30:59 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:30:59 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:31:00 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:31:00 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:31:31 rangiroa kernel[0]: disk1s2: I/O error.
May 25 14:33:17 rangiroa kernel[0]: disk1s2: I/O error.
[ad lib]
You know what that means my friends? Yes, hardware problem. OK, that disk had Time Machine backups for 3 Macs on it, but I don't use them as real backups, more like a local failsafe: the real backups are done manually on dedicated USB HDD and stored elsewhere.
But, still, I wanted to see if I could save the content of the disk.
So, I tried repairing the drive with Disk Utility, but it always failed halfway through with the dreaded "I/O error". Damn! I tried to copy the sparsebundle images (used by Time Machine for storing the backup) off to another external hard disk, but you guess what happended.
Then I let the HDD for a while and came back to it the next morning... and this time the copy of the biggest sparsebundle (207GB) failed at 10%, while previously it would fail after a couple GB... But then when I tried again right after, it failed immediately. So I tried suspecting a heat problem. I let the drive cool down for a few hours, put it in the fridge (if you put it in the fridge while hot, there's gonna be condensation), and after a couple hours, took it out and plugged it into the MBPro... this time the copy failed at 50%!
So the heat was the problem, but when you need to copy a 200+GB disk image, you can't do it by small bits, so I couldn't let it cool on a regular basis.
Then I got an idea: I grabbed a plastic basin, laid in it a large freezer block and put carefully on it the HDD without it's plastic enclosure, like can be seen in the picture below.
The freezer block generates cold for a long time, and keep the air around the HDD pretty cold, and it produces very little condensation, which means you don't end up with a fried HDD in a pool of ice water. And it did work, meaning I was able to copy the two Time Machine sparsebundles over to an external HDD (that's 207GB and 55GB), without any error or problem (OK, I had to swap the freezer bloc for a new one fresh out of the freezer after a couple hours, since it had melted inside and wasn't generating enough cold anymore). Just to be sure, I then checked the HDD again with Disk Utility and got no error. I then formatted the HDD and it is now ready to be shipped back to Western Digital's Customer Service for replacement, and my backup files are on a new HDD, plugged into the Time Capsule and doing their job like nothing happened.
So, if your hard disk gets too hot, just chill out and remember the freezer blocks.
