Installed and tested over the last few hours...looks good so far. Detected IDLE_B mode instead of an unknown power state of the disk when HDPARM was reporting UNKNOWN state (it also doesn't support the new modes) and a SMART check triggered.

My older Seagate Barracuda 7200.14s (x4) and my single remaining Seagate Barracuda Green seem perfectly happy with this build as well. 

Thanks for your help with this Nish :-).

Abbreviated syslog below:

Jul  9 11:56:50 yggdrasil systemd[1]: Started Self Monitoring and Reporting Technology (SMART) Daemon.
Jul  9 11:56:50 yggdrasil smartd[20542]: smartd 6.5 2016-01-24 r4214 [x86_64-linux-4.4.0-22-generic] (local build)
Jul  9 11:56:50 yggdrasil smartd[20542]: Copyright (C) 2002-16, Bruce Allen, Christian Franke, www.smartmontools.org
Jul  9 11:56:50 yggdrasil smartd[20542]: Opened configuration file /etc/smartd.conf
Jul  9 11:56:50 yggdrasil smartd[20542]: Drive: /dev/disk/by-id/ata-FM-25S2S-120GBP2_GS011334308M161641, implied '-a' Directive on line 169 of file /etc/smartd.conf
Jul  9 11:56:50 yggdrasil smartd[20542]: Configuration file /etc/smartd.conf parsed.
…
Jul  9 11:56:50 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], opened
Jul  9 11:56:50 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], ST8000AS0002-1NA17Z, S/N:Z8408DQT, WWN:5-000c50-086e33fa6, FW:AR13, 8.00 TB
Jul  9 11:56:50 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], found in smartd database: Seagate Archive HDD
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], ATA settings applied: Standby:242
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], is SMART capable. Adding to "monitor" list.
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], state read from /var/lib/smartmontools/smartd.ST8000AS0002_1NA17Z-Z8408DQT.ata.state
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], opened
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], ST8000AS0002-1NA17Z, S/N:Z8408TYD, WWN:5-000c50-086e3b71c, FW:AR13, 8.00 TB
Jul  9 11:57:00 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], found in smartd database: Seagate Archive HDD
Jul  9 11:57:11 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], ATA settings applied: Standby:242
Jul  9 11:57:11 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], is SMART capable. Adding to "monitor" list.
Jul  9 11:57:11 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], state read from /var/lib/smartmontools/smartd.ST8000AS0002_1NA17Z-Z8408TYD.ata.state
…
Jul  9 11:57:11 yggdrasil smartd[20542]: Monitoring 8 ATA and 0 SCSI devices
…
Jul  9 11:57:22 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], state written to /var/lib/smartmontools/smartd.ST8000AS0002_1NA17Z-Z8408DQT.ata.state
Jul  9 11:57:22 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], state written to /var/lib/smartmontools/smartd.ST8000AS0002_1NA17Z-Z8408TYD.ata.state
…
Jul  9 13:57:27 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], is in STANDBY mode, suspending checks
Jul  9 13:57:32 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], is in STANDBY mode, suspending checks
…
Jul  9 15:57:27 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408DQT [SAT], is back in IDLE_B mode, resuming checks (1 check skipped)
Jul  9 15:57:32 yggdrasil smartd[20542]: Device: /dev/disk/by-id/ata-ST8000AS0002-1NA17Z_Z8408TYD [SAT], is back in IDLE_B mode, resuming checks (1 check skipped)