In SoftRAID you can see each disks identifier in the disks tile, like disk3, disk4, etc.

Paste this command into the terminal:

iostat -w 2 disk3 disk4 disk5 disk6

(or whatever your disk numbers are)

then go to SoftRAID and Select all 4 disks and "verify disk".

Each should be doing the maximum reads. This is the fastest theoretical speed your system can do, if you add the 4 numbers together.

Correct - mounted with all data present.

Disk activity shows reads at 25-30MB/s.

Additional info - I cancelled a validation to try a new cable first (validating time remaining is 350-400hrs) and that was the start of the issue with the drives not recognized in one of the two enclosures.

This indicates the volume is mounted. Correct? All your data is available at present?

While it is validating, which is mostly reads, open Activity Monitor, and click on the disk tab. Are you getting good read speeds? (this is outside the file system, which may tell you whether this is a hardware issue, or a file system issue)

PLease attach a SoftRAID tech support file and I can take a look, and hopefully see some clues.

Tried a different cable (another tech support here said cables could be culprit for usb-c 10bps enclosure), then all drives would not show up in softraid, would not appear in disk utility, tried 2 additional cables, no luck. Rebooted, no luck. Swapped all drives to identical 2nd enclosure and rebooted and drives appeared. Running validation now "validating, waiting for mount, incorrect parity blocks: o" and no update so far after 10 mins. 

So, that's my situation on the drive mounting/not mounting but would like to solve the slow read speed issue and can open another thread if needed.

Thanks!

I am asking as I see another case where a volume is not mountable in Big Sur, but mounts OK in Catalina.

From what I can see the volume header is damaged. If you can connect to any other older mac, without SoftRAID, just to see if it mounts, it will be worth finding out.

I don't think so, but it is worth the try.

Both on Big Sur. 

Is it also on Big Sur? (Or Catalina?)

hooked it up to a MacBook Pro 16 inch.  Didn’t work. Not older but the only thing I have.