I built a Home server about a year ago, Installed a H730P with 8 6TB Drives and setup RAID 6. It's been working flawless up until about a week ago I started to notice very slow transfer speeds (less than 1mb/s). I checked in the Dell Storage Manager program and no drives have any SMART error's. I have a backup of 90% of data on the RAID. 

In the error log 1 Drive gets a lot of PD Reset error's and the rest of the log is filled with Unexpected Sense and Link Restored information logs. 

Is there a way to individually test the drives to determine which drive is causing the problems?