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  • Writer's picturekyle Hailey

MacOS disk pain

Updated: Jan 31


I was getting the following errors trying mount, umount, erase, or do anything with a Seagate disk plugged into my MacOS 13.2.1

  • Error (-69879) - can't open disk

  • Couldn't Open Fix 'Couldn't Open Device 69877'

  • error -69854,

The solution was simply to used dd on it.

I was unable to mount the disk but when I ran "dd" it gave an error like it was mounted. Trying to unmount gave an error.

So I unplugged it then ran the following in a loop:

sudo dd if=/dev/zero of=/dev/disk4 bs=1m

and then plugged it back in , thus when the disk was visible but not mounted, the dd command ran successfully. If I waited to run the dd command, the system would automatically mount it and not let me unmount it, and dd would fail to run.

After the "dd" command, I was able to "erase" option from disk utilities.

I'll to write more on this later, but wanted to a least leave a paper trail ASAP.

Found this issue extremely troubling. I mean the disk was there. Why couldn't Mac just erase it with Disk Utility? Why was the disk not erasable or mountable in the first place?

My future plan is just to have mirror of it.


Background on the story

Bought two seagate external drives to mirror and back everything up on.

The disk connections are USB cables. Why not use wireless NAS system?

I once bought a NAS disk system that all my tech friends were raving but at one point was unable to wirelessly mount the disks, and there was no way to plug the disk directly into my computer. I tried taking disks out and mounting them in a external system but they weren't readable directly plugged in makes some sense at there was some level of RAID, though I don't recall. I tend to stay away from RAID 5 and go more for just mirroring. After getting burned by the NAS system I decided I wanted straight external disks and after issues with RAID, I figure I'd just get two disks and mirror them myself. Bought a couple of these

They hooked up fine. I did have a couple of small issues have forgotten. The big issues where I lost one of the whole disks completely , which is an unsettling issue ...

I loaded all my files on one disk fine. Took a while, but got it all there.

I started loading stuff on second disk but didn't finish and put it on hold to think about an automated way of mirroring. Seagate came with an option in their tool kit but haven't looked yet. Anyway, I used the first disk a lot, which meant a lot of unplugging and plugging of cables and often the Mac was annoying slow at recognising the disk. A real wet blanket on any little flames of work motivation I had.

So I'm thinking there has to be a way to mount the disk over wifi so I can connect to it anywhere in my apartment with out a cable.

I googled but didn't find much. I saw references to hooking USB devices into a router and that should work. There was disconcertingly little info in the way of details and cookbook steps of what to do. So I ordered a router. Did an amazon search by top customer review for routers with USB ports. WHen it came, there was no USB port! Not sure what happened, I think on the Amazon page for the router, there were 4 variations offered and I must have picked one without the USB port UGH

So ordered a new router with USB port.

Plug the seagate disks and no go. There were no where to be seen.

Turns out that only ExFat disks are visible on the router when plugged into USB port on the router.

OK ,that's why I had to erase the disk which refused to erase with disk utility, thus had to use "dd" to zero out the disk, then erase worked.

Loaded up the disk , plugged it into the router, and woohoo it was visibible.

Now tried to write to it. No go. Disk was 700 permission, doing chmod 777 did nothing. No errors. No chmod change.

Turns out, that the disk has to be 2TB or less to be write-able. WTF.

Why isn't this stuff like cookie cutter cook book.

So had to erase the disk and repartition it.

$ diskutil list
/dev/disk4 (external, physical):
   0: GUID_partition_scheme 8.0 TB disk4
   1: EFI EFI 209.7 MB disk4s1
   2: Microsoft Basic Data Exfat Seaga 8.0 TB disk4s2

$ diskutil partitionDisk /dev/disk4 4 GPT exFAT Partition1 2TB exFAT Partition2 2TB exFAT Partition3 2TB exFAT Partition4 2TB

Now all four 2 TB partitions are visible and write-able.

Jeezus, seems this would be something that everyone does and it would be a well trodden path. Guess not.

Now I have to again copy over 4TB or so of data which takes about 36 hours on my laptop.

Imagine there is a faster way to do it, but what ever.

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