I've been successfully running Unraid since september of last year. Recently though, I lost first one cache drive, then shortly after my 2nd cache drive. After several reboots, I swapped cables to no avail. I then changed which ports I plugged into the Gigabyte GA-Z77X-UD4H and the drives would come in and out. I then got a 2 port ASM1061-based PCI card to connect the drives. Also, I purchased new SSD drives to see if the drive(s) were the issue. After new SATA card and cables and drives, I am able to see the new drives but after installing my 1st docker (Plex) and then trying to add a new library I lose the drives shortly after. I am at my wits end to figure out what the heck is going on with my system. Any help would be greatly appreciated. I have attached my diagnostic file.

tower-diagnostics-20190412-2047.zip

Both SSDs are dropping offline:

Apr 12 20:38:22 Tower kernel: ata8.00: exception Emask 0x10 SAct 0x0 SErr 0x90002 action 0xe frozen
Apr 12 20:38:22 Tower kernel: ata8.00: irq_stat 0x00400000, PHY RDY changed
Apr 12 20:38:22 Tower kernel: ata8: SError: { RecovComm PHYRdyChg 10B8B }
Apr 12 20:38:22 Tower kernel: ata8.00: failed command: FLUSH CACHE EXT
Apr 12 20:38:22 Tower kernel: ata8.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 12
Apr 12 20:38:22 Tower kernel:         res 40/00:5c:c0:24:04/00:00:00:00:00/40 Emask 0x10 (ATA bus error)
Apr 12 20:38:22 Tower kernel: ata8.00: status: { DRDY }
Apr 12 20:38:22 Tower kernel: ata8: hard resetting link
Apr 12 20:38:22 Tower kernel: ata7: SATA link down (SStatus 0 SControl 300)
Apr 12 20:38:28 Tower kernel: ata8: SATA link down (SStatus 0 SControl 300)
Apr 12 20:38:33 Tower kernel: ata8: hard resetting link
Apr 12 20:38:33 Tower kernel: ata8: SATA link down (SStatus 0 SControl 300)
Apr 12 20:38:38 Tower kernel: ata8: hard resetting link
Apr 12 20:38:38 Tower kernel: ata7: SATA link down (SStatus 0 SControl 300)
### [PREVIOUS LINE REPEATED 1 TIMES] ###
Apr 12 20:38:44 Tower kernel: ata7.00: disabled
Apr 12 20:38:44 Tower kernel: ata7.00: detaching (SCSI 7:0:0:0)
Apr 12 20:38:44 Tower kernel: ata8: SATA link down (SStatus 0 SControl 300)
Apr 12 20:38:44 Tower kernel: ata8.00: disabled

Could be a cable problem but since both devices are getting disabled at the same time it's more likely a controller problem, unless they share a SATA power splitter or similar.