"Does this mean there are three pairs, and I could lose one disk out of each pair?" Yes, it is data striped across three mirrors. "Is there no way to demote one of the drives (or two I guess for Raid 10, has to be even number in total), and make it a hot spare, without deleting the whole virtual disk and losing all data and starting over?" No, there is no way to do that:  1) you cannot convert/reconfigure an array to have less physical disks or total space, and 2) PERC's do not support migration/reconfiguration TO or FROM "nested" RAID levels (10/50/60), even to add disks/space.
I set up my R710 with RAID 10, six 2TB drives.  Does this mean there are three pairs, and I could lose one disk out of each pair? Also, I did not set up a hot spare first.  Is there no way to demote one of the drives (or two I guess for Raid 10, has to be even number in total), and make it a hot spare, without deleting the whole virtual disk and losing all data and starting over? Thanks for any insight anyone has on this!
R710 - how is RAID 10 working with 6 drives exactly?