Hi Ed,
Before I tried your idea, I'd make a system-image-backup of the server over the local network to another computer with the free and simple AOMEI program:
https://www.majorgeeks.com/files/details/aomei_backupper_standard.htmlThen I'd restart the server and go into whatever RAID program is running and make sure that both drives came up healthy.
Finally, I'd pull one drive, disable the RAID, and try the W7 to W10 upgrade . . .
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As I've mentioned, there can be complications on apparently identical computers doing the upgrade.
Most often, the upgrade ends with an error and claim that the computer can't be upgraded.
This can usually be fixed by an in-place repair-install that upgrades a subtly corrupt W7 system to W7 again, preserving data, programs, and settings.
Sometimes the in-place repair-install will also refuse to run, which can usually be repaired with driver updates, tweaking.exe, and startup settings.
After the upgrade, the new W10 system may work but refuse to install new W10 updates.
Which can be fixed by a W10 in-place repair-install (even though W10 was just installed, this is the fix).
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If the upgraded single non-RAID drive ran the office normally, I'd plug the second drive back in, enable RAID, and let it rebuild.
If anything ugly went wrong, I'd be glad to have the system-image-backup waiting on another computer.
Cheers,
Carl Fogel