Hello,
I have the same problem with the SATA 3, 4 and 5.
They where failing very often and the RAID 6 was falling and I had to rebuild. But on the last days they don't even powerup.
I've tried repluging everything with no success.
I'm using 4 new seagate's Red 4TB with Raid6 ext4 and one M2 SSD WD Blue.
[ 2.986119] ahci 0000:01:00.0: version 3.0
[ 2.986158] ahci 0000:01:00.0: enabling device (0000 -> 0002)
[ 2.986781] ahci 0000:01:00.0: SSS flag set, parallel bus scan disabled
[ 2.986883] ahci 0000:01:00.0: AHCI 0001.0301 32 slots 5 ports 6 Gbps 0x1f impl SATA mode
[ 2.986896] ahci 0000:01:00.0: flags: 64bit ncq sntf stag pm led clo pmp fbs pio slum part ccc apst boh
[ 2.990725] scsi host0: ahci
[ 2.991508] scsi host1: ahci
[ 2.992139] scsi host2: ahci
[ 2.992767] scsi host3: ahci
[ 2.993387] scsi host4: ahci
[ 2.993618] ata1: SATA max UDMA/133 abar m8192@0xfa010000 port 0xfa010100 irq 91
[ 2.993629] ata2: SATA max UDMA/133 abar m8192@0xfa010000 port 0xfa010180 irq 92
[ 2.993639] ata3: SATA max UDMA/133 abar m8192@0xfa010000 port 0xfa010200 irq 93
[ 2.993649] ata4: SATA max UDMA/133 abar m8192@0xfa010000 port 0xfa010280 irq 94
[ 2.993659] ata5: SATA max UDMA/133 abar m8192@0xfa010000 port 0xfa010300 irq 95
...
[ 4.280968] ata3: SATA link down (SStatus 0 SControl 300)
[ 4.592768] ata4: SATA link down (SStatus 0 SControl 300)
[ 4.904777] ata5: SATA link down (SStatus 0 SControl 300)