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How to use a SoftRAID startup volume with High Sierra

If you're using High Sierra, and booting up from a SoftRAID volume, you'll need to follow the steps given in this forum post, since the macOS High Sierra Installer does not recognize SoftRAID volumes as valid startup volumes.

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Validating & Verifying Mirrors
I'm a cautious engineer who's upgrading from SoftRAID4(X.6.8) to SoftRAID5(X.6.8 & X.12.6); I always run the previous OS and buy mature hardware - hence my love of 2010-12 Mac Pros with eSATA external hard drives.

I'm converting SoftRAID4 three-disk RAID1 mirror volumes to SoftRAID5. Before I update the drivers to SoftRAID5, I wanted to check the status of my mirror volumes. (I know this is perhaps overly cautious, but once you're in deep poop it's too late.)

I plan to mount all three disks and validate each volume (SoftRAID4 on X.6.8), then split off the third disk as a Read-Only Secondary, then on another machine (running SoftRAID5 on X.12.6) update the disk driver on the two-disk mirror (holding the ROS disk as my backup).

Q#1 Validating three disk mirrors takes some time, so can I restart the machine in the middle of a <Volume >< Validate> operation without losing my place (like Certify) does?

Q#2 Let's say that SoftRAID4 reports an error on validate. If the volume is a 3-disk mirror will it report which disk fails to compare to the other two disks and the offset (or will it use some primary-secondary disk logic here)??

Q#3 Should an error occur, the first thing to check is cable communication issues. I hunt those down every time and repair/replace so my eSATA hardware is historically solid. I think the next thing to do is to run disk verify on each of the three disks and note the offsets of any errors to conclude which disk has faulty media and check the offset against the validate error. Is this the logical second step here?

Q#4 Lets say the error points to disk B being bad at offset 123 456 789. Can you describe the method to tell which MacOS filename is located at 123 456 789???
I stopped programming in UNIX 20 years ago, for the same reason that I don't use a chainsaw (My wife the ER nurse has told me enough stories to conclude that unless you're sufficiently skilled bad things can happen very fast.) So I'm thinking some higher level tool; though I could dabble in terminal.

Q#5 Do you have any suggestions on my overall "validate before update" plan in general?

Q1: Generally yes, we try to pick up, but it does not always happen. Let it validate overnight though, that should be plenty of time. And optimize for server to get it completed faster.

Q2: Yes, you will see the disk# and offset in the log. If you give your disks labels (as in v5), then you now which disk more easily.

Q3: If you validate, there is generally no need to also verify the disks, though.

Q4: No. There used to be an app called File Xray that could do that. We do not have that ability.

Q5: Its fine, you can also just run 5.x and validate. The transition should be seamless.

Best is make sure you have a backup (offsite mirror is OK), then you are good.

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