RAID Horrible Perfomance  

I have 8 6TB Seagate SAS 12GBps drives, I tried to use a Perc H730P and a SAS 9300-8i, with the 730P I created a RAID 6 initialized, formatted in windows and tested. using CrystalDiskMark I got 800mb Read but only 100write speeds. But whenever I tried to copy files is was extremely slow would start out around 200mbps and then within seconds drop down to 10-20mbps. Something didn't seem right so I tried the 9300-8i card and tested each hard drive individually. All of them scored 210-220 read/write speeds. I then created a Parity Pool with Storage Spaces, and got similar results as they 730P. Copied files from my NVME (60GB File and 7GB File) started fast and then dropped to 10-20mbps. Once the files were on the Parity Pool I tried to just copy/paste and still got slow results.

Am I doing something wrong here? I'm not sure what else it could be, these are all new drives.

AOG Strix B550-F Motherobard/ NVME Win 10 OS/ 64GB RAM/ Ryzen 7 3800X
Here's a link to the cables I'm using
https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

Does your Perc H730P have a write back cache battery installed?

Yes

So, if it has a battery and the battery is working/charging, what do your write back cache settings look like in the controller? Do you have writeback caching enabled? It sounds like write-through is enabled!

Here's Screenshots

Your strip size is to small. 64KB is alright for database loads but won't cut it for tasks like archiving or backup. Not sure what your data load is here.

In general you will get better performance in Storage Spaces if you do not use Parity. Storage Spaces cache is designed to handle write data in a dynamic fashion meaning that dependent on the data stream write cache will scale with demand. In practice this does not seem to work well except when using Storage Spaces Direct, tiered storage, and storage clustering.

With raid cards and these large capacity drives where sector size is 4096K it pays to increase the stripe size. The most effective is 512KB as these drives firmware effectively make them 512e drives so if you write big chunks of data at 512 or higher rates your performance will increase. Still, with parity performance will suffer.

Thanks, I'll try to change to 512KB and see if that helps. I need parity and don't expect extreme performance but still expected at least 200-400mbps. Just a simple HomeServer for streaming Plex to multiple clients and backing up photos/videos/etc

Well, your stated data will mostly be large file sizes so increasing stripe size should help. Reaching 200mbps-400mbps should be no problem. I myself run a Storage Spaces tiered storage pool where a mirrored set of SSD's cache a larger Parity tier of large HDD's. I can push data at around 130MBps to 150MBps quite easily. The entire Storage Spaces drive pool is set to use 4096 cluster size because all the drives are 4096/512e drives.