If you de-allocate the spare drive, you should be then have an option to "Migrate RAID/stripe size" and migrate it to RAID 5 (as long as you have at least one available drive) without data loss.
Then do a logical drive expansion once the RAID level migration finishes. Finally, you'll then be able to expand the partition in whatever OS to use the newly available space on that logical drive.
Do NOT delete the existing RAID 1+0 array... you shouldn't need to do that. You should be able to do an online expansion with the system running, although you'll have some drive slowness while that expansion happens.
If you're not worried about the impact, you can change the "transform" and "rebuild" priorities from the default "medium" to high. Or set it to low if performance is a concern, it'll just take longer.
I've done this plenty of times in the past but I'm going from memory since I don't have any systems with an extra drive available to actually confirm the step-by-step process, but it is fairly straightforward.
Then do a logical drive expansion once the RAID level migration finishes. Finally, you'll then be able to expand the partition in whatever OS to use the newly available space on that logical drive.
Do NOT delete the existing RAID 1+0 array... you shouldn't need to do that. You should be able to do an online expansion with the system running, although you'll have some drive slowness while that expansion happens.
If you're not worried about the impact, you can change the "transform" and "rebuild" priorities from the default "medium" to high. Or set it to low if performance is a concern, it'll just take longer.
I've done this plenty of times in the past but I'm going from memory since I don't have any systems with an extra drive available to actually confirm the step-by-step process, but it is fairly straightforward.