RAID 5 is old technology that isn’t ideal for big drives like we have these days. RAID 5 basically allows you to lose 1 drive but if you lost/lose a 2nd drive all is lost.
RAID 6 allows you to lose 2 drives without loss of data but if you lose the 3rd drive all is lost. Both of these may not sound bad but what happens when you have a drive go bad and then are in the rebuild phase with a new drive and the extra work of the rebuild causes another drive to fail? This happens a lot more then people realize.
RAID 5/6 have their place in business when working with small files like documents, Xcel files and business apps since the overall storage doesn’t need to be big (rebuilds can be fast). This changes when you are basically trying to build storage solutions.
The problem with RAID 6 for the OP is that he’s thinking of adding a 4 bay NAS. Well if 2 bays are needed for RAID 6 that only leaves 2 bays for data. He might as well just mirror the data and be done with it.
RAID systems make a bit more sense when you have 8 drive bays as that leaves more drives for data. RAID systems can come with limitations that cause many people untold issues when they try to expand storage as they need to rebuild the arrays which takes longer and longer the bigger you get.
I’ve been down this road to many times and now just prefer KISS (Keep It Simple Stupid). I run windows and mount drives (local, USB3, NAS or File Server) as local drives on the Plex Server. So with say 20 drives if I loose 1 drive I’ve lost 1/20th of my storage and never all data at once. I use DrivePool to group multiple drives into one drive letter (makes everything look like 1 giant drive like RAID can) which makes plex setup easy as well as FTP servers or just accessing my media over the network.
For backup or redundancy I use the free opensource SnapRAID (not raid at all) to create parity of all my drives (local or network). For me this works awesome as I can add drives any time I want and size of drives doesn’t matter. I can pull a drive and move it to any other computer and access it normally since it’s not a proprietary drive format but just good old NTFS…
With SnapRAID I can have from 1 to 8 drives used for Parity and I can add a new parity drive anytime I want for additional redundancy.
So the OP could purchase a 4 bay drive NAS or just a direct attached storage and populate it as needed with additional drives one at a time and keep using the 2 USB3 drives he already has for maximum flexibility in drive space. He could start with 1 drive parity and then add a second drive later when ever he wanted.
Again, like I said in my first post there isn’t a best way but there are many ways but RAID 5 is just bad for media files and arguable RAID 6 is bad as well or just not as ideal.
