I have a mac mini (Mid 2011) running High Sierra (10.13.4) that I've been trying to use a home server. I'm not sure what the cause is, but my external USB drive (a 3rd-gen 4-drive Drobo) keeps disconnected after 16-48 hours. The Drobo is out of warranty and since June 2017 Drobo doesn't provide any community support so I haven't been able to figure out if the issue originates with the device. Aside from power cycling (which isn't the cause in my case) what might cause a USB drive to disconnect ?

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    Speaking from personal experience, I literally banned Drobo from our organization because of their high failure rate. More often than not, they would just stop functioning and we ended up losing data. This may be an issue with the Drobo and not the Mac. – Allan May 22 '18 at 7:35
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    I love my Drobo but you do need to keep an eye on it. You will need to replace the fan at some point. The Drobo will disconnect from time-to-time, I never found a solution to that so moved to a 5N. You can try setting your computer to never sleep and the drive to never sleep. That helped limit the disconnects for me, but did not solve it. – Dave Nelson May 22 '18 at 13:38

Are you using the USB cable that came with the Drobo? I know I got a bad one with my Drobo 5D that Drobo had to replace. I also recall some discussion a few years back about issues with Drobos sometimes disconnecting when the host went to sleep. Is your Mini set to never sleeps do not to sleep the connected drives?

I’m using a Thunderbolt connection with my 2012 Mini so my only USB/Drobo experience is a 5D with Windows 10.

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    This is actually a replacement unit. The original device I had failed a few months after purchase so Drobo replaced it under warranty. I'm using the cable that came with the device. The cable is thicker than most USB3 cables I've seen and feels quite sturdy. – Ivar May 22 '18 at 23:57

I know this is an old thread. I have a Drobo 5C (replaced a Drobo 3rd Gen unit). This is apparently (according to Drobo) due to an issue in MacOS when the display goes to sleep. According to Drobo, Apple starts sending a barrage of USB packets aggressively pinging the USB connected devices as part of their technology to ensure that any device plugged in while in sleep mode is not automatically mounted. According to their tech, this high volume of ping type packets causes issues that results in the Drobo going offline.

I do not know yet if I agree with this. I have turned off all power management, and still experience the issue. I had backed up all my data to a Seagate USB 3 drive, and reset my drobo. During the restore, I ran multiple rsync jobs to restore the data as aggressively as possible, and the Drobo ejected itself again. I then ran a single rsync job to restore the data, and it did not disconnect.

My theory, is that Time Machine tends to backup when the computer is sleeping. This backup is rather aggressive, unlike rsync, and that the Firmware in the Drobo is poorly written, resulting in buffer overflows, and thus the drive ejects itself.

When the data stream is slow enough, this does not seem to happen, which supports this assertion. If this is the case, 7200 RPM drives would more be desirable for the DAS even though 5400 RPM drives are the norm for longevity. I do not have the drives to test this theory out, however, Drobo had suggested that although desktop drives are fine (mine are actually DVR drives), they recommend NAS drives, and the Seagate RED.

  • thanks for the update! much appreciated! – Ivar May 30 at 16:03

The bad and the good cable looked identical but tech support could tell the difference with the part number on the cable.

I had some initial teething pains with Drobo but it has been sold for the last couple of years.

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