RAID/RAM/4th HDD Blank

[Enquiries]

In your Setup Guide YouTube video series, you never addressed why you left the fourth drive unformatted in the series (I watched all 10 setup guides). You used 4 HDD's, formatted three of them with RAID 5 and said you were leaving the fourth one for showing what to do with it in the next video. My questions:
1. Why RAID 5 instead of SHR-2 (my understanding is with SHR-2, I can replace one HDD with a bigger one and gain more space, Can't do that with RAID 5)
2. What are you doing with the fourth drive that is not in the RAID 5 configuration?
3 . you mentioned that we should wait to install the extra RAM until after we setup the RAID and DSM. Why? I haven't started using it yet and I can reset and remove the RAM if it really makes a significant difference and start over. Thanks for your help and your setup videos.

[ed]

Yes, SHR will allow you to mix different size drives. Regular RAID do not allow that.
The spare bay can be used for hot spare drive. If RAID fails, a spare drive will be automatically introduced and damaged drives get disconnected. A spare bay can also be used for caching.
You can install RAM at the start. But statistically having an updated operating system beforehand allows RAM upgrade to happen with no problems. But if it works already, there is no need to worry.

I hope this helps.