Advice please: Scanning for bad sectors

[Azathoth]

A couple of the photos in my photo collection are corrupt, on both my MBA, Time Machine copies and independent external HDD copy.

I would like to run some disk scanning software on the internal SSD, external USB drives that I have (and if possible on the NAS, a AFP mounted embedded Linux box).

Any free utilities for this - something like chkdsk that exists since the dawn of time on windows? I've googled without success.

I'm happy to work in the terminal, and have MacPorts available.

Any suggestions?

PS. Please don't mention SMART - this is not the same as a surface scan.

 

[John T]

Are you sure it's not the camera?

 

[Makosuke]

If all the backup copies are corrupt, then you know for a fact that the corruption happened somewhere near the beginning of the chain, so there's no point in integrity checking anything but your main hard drive. And it's also, as mentioned, possible that they came off the card corrupt--do you know for a fact that they were good when you originally copied them from the camera to your computer? (And if not, what brand of memory card do you use in your camera?)

It's worth mentioning that if there are bad sectors, there is usually a VERY long delay while the hard drive attempts recovery on the data it can't read when you access the bad files. If they open instantly but are corrupt, it's possible that the drive already remapped the bad blocks, but it's also quite possible that the corruption has nothing to do with the surface of the drive.

Regardless, I'd try Drive Genius; I've used it at work with some success to diagnose directory problems, it's not very expensive, and it includes a surface scan feature. Techtool Pro is another, beefier, more widely-known package I've used (Apple included a basic version with AppleCare back in the day), but it's a bit more expensive. There are several other pieces of software available (none free that I'm familiar with), as well.

Google also turns up at least one article on a free unix tool that'll test for bad blocks, if you prefer DIY, but you can of course search for yourself.