Spurious Bad Sector Errors and reversing the USB plug

I was getting “unable to save due to bad sector errors” messages.
This is a 5C with 5 12 T drives, and about 10 T of data stored on these 5 drives. Plenty of unused space.

I’m using “Dual Drive Redundancy”.

I ran CHKDSK /r and after 250 clusters checked, out of 980,000, I got the error “the disk does not have enough space to replace bad clusters”. Which would mean massive failures on most of the drives. Unlikely.

Drobo suggested I reverse the orientation of the USB cable. Which is puzzling, since the plug is rotationally symmetrical.

I did that, and a new CHKDSK has been running for 4 days, no errors reported, and has checked 390,000 out of the 977,000 clusters.

I’m assuming the rotated USB plug fixed something. I asked DROBO for some details, but haven’t gotten an explanation.

In the mean time, CHKDSK will take another 5 days to check all 60 T’s of data. I’d like to get back to work on the DROBO, but I’m concerned about what’s really going on.

The “bad sector” report seems spurious.

Does anyone have any technical explanation for what’s going on?

Thanks in advance.

Actually, it seems to matter, mine goes into USB2 mode unless it’s the “right way”, can’t say I like USB C for that reason, Drobos aren’t the only case where strange things happen according to the orientation of those plugs.

Not entirely sure how CHKDSK reacts to the /r switch on thin provisioned space, Drobo will be presenting the same “free” sectors multiple times… So while CHKDSK does other things, the free space check is useless on a Drobo.

I’d be inclined to check the drives individually out of the Drobo, a long project I know, read out the SMART data & suspect any with pending sectors or big counts of reallocated sectors as a quick first triage.

I might even close down, & run an actual scan on the pulled pack under Linux, drive at a time (you’re looking days per drive sadly to do that) but badblocks non-destructive write test won’t damage the data on a healthy drive, if you get errors you know which drive is the culprit, you do have to be extremely careful with the command line switches using badblocks, losing everything is quite easy.

I’d be disinclined to pull drives individually, in case there is a faulty one & it messes up during rebuild by being one of the ones still in there.

Back up your data first!

It looks like the drives are fine; no errors after 40%.
Since before I switched orientation, I was getting a plethora of errors, it was probably a communication issue.

It was reporting as bad sectors, since it couldn’t write to the drives. It doesn’t know how to differentiate between a cable and a sector!
I killed the CHKDSK and remounted the Drobo.

Saves are fine, so far.

It’s still reporting to the OS as USB 2, so I suspect the cable itself has problems.

Thanks for your thoughts.

No “bad sector errors”

  1. The “faster with USB 3.0” message was still present

  2. I was only getting about 25 MBS reads, total

  3. Everything; reads and writes, was slow, whether feeding a direct attach, or over a network to OSX.

  4. I replaced the cable with a new one I had around. (Just swapped the cable; didn’t reboot the OS or the Drobo)

  5. Still seeing the “faster with USB 3.0 message”

  6. Shut down Drobo

  7. Shut down CPU

  8. Restarted CPU and Drobo

9, USB 3.0 warning in Settings no longer there

  1. After 10 minutes Drobo reported 1 drive bay empty - drive still in place

  2. Data Protection run in progress

  3. I reinserted drive that was reported missing.

  4. Drive now recognized

  5. USB 3.0 warning reappeared

Robert J. Steinberg


617.448.4961 Cell


With a new cable, upon reboot, Drobo is using USB 3.0, but quickly reverts to 2.0

This is true with a replacement cable, and with reversing the cable end

Maximum I/O through Photoshop, latest version is 40 MBPS reads of a 900 MB .psd file

Same file (for comparison) from a SSD is 82 MBPS.

Is this an expected performance?

I’m concerned about the reversion to USB 2.0.

By all means check my research but something around 40MB/s is about expected for an external USB3 enclosure, be it Drobo, some other DAS unit or a plain old external drive. It’s slightly more than the best I ever see on my 5C & USB TreeView shows that as connected & working on USB 3.

Just the information I was looking for.
Thanks so much!