Thanks trurl for the reply!
I did get the concept that UnRaid is not RAID, that nothing is stripped, in fact that was the reason that convinced me to go for UnRaid because I have a lot archive data that just need to sleep on non-spinning disks! I did solved the problems for my huge archives of media, that is not my concern anymore.
Now I am dealing with the problem of running VMs with decent performances. My 5 VMs are stored on a single WD Red and they a limited to very slow reading speeds. When I do a lot of parallel reading operations from all my VMs, like starting all of them, it is not smooth at all.
I am still not sure about my upgrade path. Having a single SSD SATA part of the array should in theory delivers reading speed of 500 mb/s and a SSD Nvme PCIe may deliver more than 2000 mb/s from that device alone. I am aware of the lag caused by the parity that needs to be calculated and then written on the parity drive, but that should not be a reading bottleneck for a SSD part of the array, I have not tested that but that is my understanding. Like I said, I would be pleased to have an SSD on the data array if I would at least gain some reading performance for my VMs, knowingly that data on those SSD won’t be striped like in normal RAID. I could do some manual file placement on several SSDs, I assume that this would give me some real reading speed benefits. As for improving writing speed a pool cache is what I am looking for. My main concern about having SSDs assigned to my array is is that SSDs are not officially supported for the data array so I may have to forget about that option.
Talking about the pool cache, knowing about other supported RAID configuration on btrfs is interesting, but like I said all the conversation are focusing on levels of protection or the size of the pool, no details about expected performances. I would like to have some numbers about how btrfs RAID 1 or RAID 0 performs. What is troubling me is that I have seen on a post that btrfs RAID 1 is not systematically reading from two mirrored devices at the same time, instead multiple concurrent OS process requesting read operations are pushing the RAID 1 pool to read from multiple devices at the same time. I am not sure how btrfs behaves. A perfect RAID 1 implementation, let’s say with two devices, would deliver reading speed of the two devices combined, leaving the writing speed not improved but my question remains:
Can we really achieve RAID 1 reading performance with btrfs?