Because this post will mark my last update on this thread after 15 months that spans all over the map, for any readers who ever see this years from now, here is the recap of all 13 pages: 

1. - macOS disk ejects upon sleep. Never resolved, just work around it now. Once in a blue moon have forgotten and had disk eject errors. Still annoyed with Apple over that one but can't do anything anymore about it. 

2 - Flex 8 hardware with disks not showing, which just sort of resolved itself and I never got a conclusive scientific answer to. Hardware replacement did not 100% solve that issue but as the fan was most certainly dead on the old returned unit, the replacement was still extremely helpful and I remain grateful. 

(2b - somewhere in there an nVME blade died without warning and suddenly but that was pretty much random and had no relation to either Apple, OWC, or SoftRAID, and once more to their full & complete credit, OWC helped). 

3 - The Seagate fully partitioned bug I finally got to the bottom of. The reason 18.4 no units seemed crushing at the time was (aside from being the third blow): The first time I saw it and just typed in "4TB" while trying to create a new volume, a SoftRAID error notification that sounded fairly grave and caused me to re-certify. Due to that event and until getting to the final answer I was afraid to ever create another new volume at all on those Seagate disks. The Toshibas and Western Digitals all purchased as additional storage/upgrades never caused any concern.

Because the WD disks didn't suffer from the bug, I only generated two Tech Support files attached. One created before volume deletion, showing "134MB" in the New Volume dialog box when the disk was truly fully partitioned. Most notably, 134MB was not 18.4-no units. Second, a support file generated after deleting that 4TB volume but not re-initializing the disk, proving that the New Volume dialog behaves normally defaulting to "4TB" and not still appearing fully-portioned, as was the case with two Seagate EXOS disks.

All those support files are saved and organized in my Documents folder but will not be attached unless requested, as I did not want to "digital litter," and this update is not an "I told you so," only verification that I got to the bottom of the conclusive answer. 

The original Flex 8 came loaded with 7 Seagate EXOS 4TB disks. Along with everything else that went wrong right after hemorrhaging $7000 on a new computer at the start of 2025 (half of which was Apple's fault and we never got an answer or proper solution on disk ejects, especially as what I went through hardly inspires me to stay up to date on new macOS releases) and the business essentially dying in no small part affected by the loss of time and productivity, I was shuffling a lot of data around. When the Flex 8 hardware issues merited replacement and OWC made an exception to help  without making me send back the loaded enclosure (which I remain forever grateful for), the 18.4-no units bug arose.

Nearing an answer a couple weeks ago after the first experiment with a Seagate EXOS, it didn't seem scientific enough to leave it at one test a year later. So I took another one one the seven that was ready for deletion and performed the same sequence of operations with that disk (which had also shown the 18.4 bug -- none of which had happened prior to 2025, prior to going to the Mac Studio, or prior to SoftRAID updates).

The identical series of events and solutions unfolded with the second Seagate EXOS. Clearing "Largest Free Block - 18.4 (no units)" required re-initialization. Deleting disk volume(s) left both Seagates appearing as "fully partitioned" until they were re-initialized. Which would explain what happened last year when I had deleted several volumes on several disks and tried to create a new volume, culminating in an error notification that scared me and led to re-certifying the entire disk(s).

Volume deletion leaves Seagate disks appearing fully partitioned and I now have absolute proof it is limited to Seagates, or at least absolute proof it is not tied to the Toshibas and Western Digitals in my collection. 

To confirm that the Western Digitals and Toshibas I kept harping on not showing the 18.4 (no units) problem, I needed to run one more test.

So just now I took a Western Digital 4TB disk from my drawer, found a volume containing 1.01TB of video footage that was ready for full deletion, and did the following:

With the volume appearing in SoftRAID and the Western Digital fully partitioned, the New Volume dialog box did not show "18.4" no units. Instead, it showed "134MB," which is the same as the Toshibas showed. 18.4-no units was indeed limited to Seagate EXOS - the ones shipped with the Flex 8 upon purchase several years ago. At this point I generated a Tech Support file of the Western Digital BEFORE the volume was deleted. 

Then I disabled the safeguard and fully deleted the disk volume on the WD. Looked in the New Volume dialog box and low and behold, it defaulted to creating a new 4TB volume. No 18.4-no units mess. Volume deletion showed that the disk was no longer partitioned. I generated a Tech Support file at that stage as well.

Did not create a third support file after re-initializing because I did not need to re-initialize the Western Digital in order to clear "18.4"-no units. 

The bug was limited to the 4TB Seagate EXOS disks and everything I kept saying about "it's not happening with Toshiba or Western Digital" turned out to be verifiably, scientifically, demonstrably true. 

So if anyone else in the future - maybe many years from now - ever sees this and is going through what I went through, try re-initializing the disk if it's still appearing fully partitioned despite full volume deletion.

And, I am sorry this took so long to figure out. It was not something anyone had ever seen and until I was able to see it in the "New Volume" dialog box directly, it made no sense what was going on. I will take the blame for that, but it is a very odd bug. 

I opened your support file, which was the state of your system when you had the problem. You were complaining about the 18.4, in THAT condition. What I did not realize was you were complaining about seeing it, but not in the main window, where I expected it, but in the "new volume" dialog box. I was able to try to create a "new" volume, and saw the 18.4 on your configuration. and, the 4 disks were "fully partitioned.

So you can replicate this easily. Just select your 4 drives, select "New Volume" and just look in that dialog box. You will see two disks with 134MB available and 2 with "18.4" no units, just as you complained.

Don't actually "create" the volume, just cancel. But that is your bug. and there is a proper explanation for it. You will never see that 18.4 on a newly initialized disk, with no volume on it. That is why I never saw it. 

I consider this "case closed". If you want to settle your mind, try opening the new volume dialog box and you will see it again.

Not to beat a dead horse but to give a conclusive and promised follow-up, I just now created four support files and will attach them beginning with the the next post in order to keep the sequence of events organized. All the writing will remain in this post in case it is ever of any use to someone else many years from now in the archives (that way you can keep this update in the thread but delete or remove the follow-ups with only the support files). Italics and bold emphasize provided for historical documentation, as I wish I'd never gone through it and would love it if someone else in the future finds answers from what I had to before I could know for sure. Now there's no question. But it involved running the following four tests:

1. First thing I did was disable the safeguard and delete both volumes. If I am clear on the terminology, with all volumes deleted and no volumes created, the disk should not be partitioned at all. In the "New Volume" dialog I still saw "18.4" no units. Either I don't understand what a disk partition is, or this validates that there was some sort of bug that made the disk appear fully partitioned even after complete volume deletion. If I'm an idiot I'm an idiot but I'm pretty sure I'm not because of what happens in the results of the fourth test later.

2. Next, I trusted the certification (first from OWC, then I did it again two years later) was good enough so I skipped re-certification and with no volumes present on this disk that was still showing "18.4" in the "New Volume" dialog box, THEN I re-initialized the disk. At that point, 18.4 was gone, and the New Volume dialog box defaulted to 4TB. (It's a 4TB Seagate EXOS which were the only disks 18.4 was happening with).  

3. Third, I created a new disk volume and checked the New Volume dialog again. At this point it defaulted to 134MB referenced in the above reply (which was based on information long gone as a year ago was ancient history and I know not what those 4 drives referred to even were anymore...but did recall this was a Seagate EXOS issue only). 

4. Last, I wanted to confirm that if I deleted the newly created volume, the disk would no longer be fully partitioned. This was specifically to confirm I wasn't off my rocker and that when you said the 4 disks were "fully partitioned" that I was not misunderstanding what partition even means, So I was ready to be wrong, but....

With the newly created disk volume deleted on the re-initialized disk, volume deletion most certainly showed the disk was anything but "fully partitioned." In the New Volume dialog box it defaulted to 4TB, no longer 18.4 no units. 

The "bug" appears to have been tied to the disk continuing to appear fully-partitioned with no volumes on it. It's over now and I'm glad but it appears deleting the previous volumes was not enough. The disk needed to be re-initialized from scratch in order to clear the 18.4 debacle. The other Seagate disks that I need the data on will forever live in their current state, as presumably the 18.4 issue isn't concerning to disk health and I keep 3 backups (including one off site) for critical data (except for when my blade died last year without a backup; ouch). 

Case-closed indeed.