Having recently purchased Backblaze, I'm currently backing up to the cloud my 4TB WD external drive (7 months old). The backup process can run without problems for a few hours (ranging between 4 and 10 or so), but will inevitably stall on I/O errors with the external drive. Running First Aid using Disk Utility returns that everything is fine. I've tried a different USB port and a different USB cable, all to no avail.

Obviously the process of backing up the entire drive is accessing sectors that I might otherwise not have accessed for a long time, and which might be corrupt. But why does Disk Utility say the drive is OK? Does it only scan the headers etc.? Might the problem actually be with Backblaze? Is the best solution here to exchange the external HD under warranty?

  • Welcome to Ask Different. Are you only getting these I/O errors when trying to do the BackBlaze backup? You don't get the errors when you access the ext drive thru Finder? – fsb Mar 12 '18 at 12:41
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    I've never known Backblaze to error like that & I've been using it for years, with several TB of data backed up. I'd be tempted to run something more 'aggressive' over the drive, TechTool Pro, Drive Genius etc & see what they say. – Tetsujin Mar 12 '18 at 12:43
  • @fsb, not that I know, but the I/O errors only show up after a few hours so haven't been able to replicate it yet manually. But, once the I/O errors show up, Finder does not show any contents on the drive any more (as in: drive still shows up and can be opened in Finder, but says "0 files") – user1092247 Mar 12 '18 at 12:57
  • @Tetsujin, apparently the drive is not SMART-supported? It doesn't even show up in Drive Scope... – user1092247 Mar 12 '18 at 16:20
  • No, there's no SMART support for an external USB drive at all. – Tetsujin Mar 12 '18 at 17:46

FWIW: As suggested by @Tetsujin, running a more 'aggressive' tool over the drive (in my case TechTool Pro) uncovered a number of bad blocks.

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