I'm on SHR-2 , 2 drives can fail without data loss. I have 8 drives in my NAS.
If I remember correctly the Synology Hybrid Raid advantage over standard raid is that you start with a couple of drives and expand as needed, mix and match drive sizes etc.
I started with 4 drives, added 2 a year later and added another two a year after that. Was very easy to expand, it did take about a week to expand the volume but happened in the background
I have 8x 16TB drives
Another cool thing about Synology is that if the NAS hardware dies, I can purchase any 8+ bay Synology, pop the drives in and it'll be running again.
Also have the option to daisy chain 3 Syn NAS together to expand the single volume
Amazing how easy it is and what it can do.
Have mine on 10gig network and read/write speeds are 400-500MB/sec
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