I have encountered a similar problem. My system spec is ASRock E3C226D2I with 16GB ECC RAM and g3240, 8GB USB stick (system boot), and 6 Hitachi Deskstar 1TB hard disks (4 of these disks came out of an older Windows 7 RAID 10, and 2 housed Windows 7 boot disks).
While installing, FreeNAS9.3 shows the following error(s). Would this error render the installed system not able to detect any of the 6 disks?
(ada2:ahcich2:0:0:0): CAM status: ATA Status Error
(ada2:ahcich2:0:0:0): ATA status: 51 (DRDY SERV ERR), error: 40 (UNC )
(ada2:ahcich2:0:0:0): RES: 51 40 30 69 70 40 74 00 00 d0 00
(ada2:ahcich2:0:0:0): Retrying command
(ada2:ahcich2:0:0:0): READ_FPDMA_QUEUED. ACB: 60 00 00 69 70 40 74 00 00 01 00 00
(ada2:ahcich2:0:0:0): CAM status: ATA Status Error
(ada2:ahcich2:0:0:0): ATA status: 51 (DRDY SERV ERR), error: 40 (UNC )
(ada2:ahcich2:0:0:0): RES: 51 40 30 69 70 40 74 00 00 d0 00
(ada2:ahcich2:0:0:0): Error 5, Retries exhausted
Loading early kernel modules:
GEOM_RAID5: Module loaded, version 1.3.20140711.62 (rev f91e28e40bf7)
savecore: /dev/dumpdev: No such file or directory
/etc/rc: WARNING: unable to figure out a UUID from DMI data, PLEASE FIX if you are an integrator.
/etc/rc: WARNING: generating a random one.
Setting hostuuid: 979a651b-08ad-11e5-acb6-d05099384afc.
Setting hostid: 0x08d5400e.
Not suitable dump device was found.
Entropy harvesting: interrupts ethernet point_to_point kickstart.
Starting file system checks:
Mounting local file systems:
igb0:link state changed to UP