It took 18 hours of disk scanning with Tech Tools Pro to uncover the hard drive bad blocks that probably contribute to some of my recent iTunes sync errors. Errors that had left me on the verge of paying $200 to repair an iPhone 4s — I’m now going to hold off on the repair until I test that iPhone against a replacement drive.
I bought Disk Tools Pro 3 years ago when my primary iMac drive developed bad blocks, so it’s paid for itself a couple of times over. Once again Disk Utility found no errors and the SMART status was “fine”.
The drive is dead, modern drives are not allowed any bad blocks. The drive's onboard computer remaps bad blocks dynamically, when they show on this kind of test the drive has exhausted its reserve. So I need a replacement.
Lately I’ve been buying Western Digital Green SATA III 5400 RPM 64 MB Cache Bulk WD40EZRX drives, a few months ago the sweet spot was 3TB, this time it's 4TB. I don’t worry about performance on this external drive — I use my internal SSD for apps that need speed. I like that these drives run cool.
I also don’t need 4TB of storage — for one thing my backup drives are only 3TB. I assume that a 4TB drive will have a larger set of remappable blocks and that’s helpful.
The 4TB capacity will come in handy when this drive gets rotated out to backup. I’m getting tired of drive failures — mine seem to last 2-3 years at best. So I’m going to start replacing my secondary external drive every 18 months. At that time if it passes a full block scan it will go into the backup pool, and I’ll junk my oldest backup drive.
PS. If iTunes were really having trouble accessing data from this drive, the polite thing would have been to write something useful to Console.app log files.