So I have started to see some fairly scary critical messages pointing at an issue with hpt_disk_1/15/1. Before I go removing hardware from my Freenas box, I just wanted to validate that my assumption is correct.
hpt_disk_1/15/1 is the same as <HPT DISK 0_15 4.00> , and is therefore da15 which is a 3tb WD with a serial no WMATV4761212
root@constellation:~ # camcontrol devlist
<DOGFISH 30G Q0707A> at scbus1 target 0 lun 0 (pass0,ada0)
<HPT DISK 0_0 4.00> at scbus5 target 0 lun 0 (pass1,da0)
<HPT DISK 0_1 4.00> at scbus5 target 1 lun 0 (pass2,da1)
<HPT DISK 0_2 4.00> at scbus5 target 2 lun 0 (pass3,da2)
<HPT DISK 0_3 4.00> at scbus5 target 3 lun 0 (pass4,da3)
<HPT DISK 0_4 4.00> at scbus5 target 4 lun 0 (pass5,da4)
<HPT DISK 0_5 4.00> at scbus5 target 5 lun 0 (pass6,da5)
<HPT DISK 0_6 4.00> at scbus5 target 6 lun 0 (pass7,da6)
<HPT DISK 0_7 4.00> at scbus5 target 7 lun 0 (pass8,da7)
<HPT DISK 0_8 4.00> at scbus5 target 8 lun 0 (pass9,da8)
<HPT DISK 0_9 4.00> at scbus5 target 9 lun 0 (pass10,da9)
<HPT DISK 0_10 4.00> at scbus5 target 10 lun 0 (pass11,da10)
<HPT DISK 0_11 4.00> at scbus5 target 11 lun 0 (pass12,da11)
<HPT DISK 0_12 4.00> at scbus5 target 12 lun 0 (pass13,da12)
<HPT DISK 0_13 4.00> at scbus5 target 13 lun 0 (pass14,da13)
<HPT DISK 0_14 4.00> at scbus5 target 14 lun 0 (pass15,da14)
<HPT DISK 0_15 4.00> at scbus5 target 15 lun 0 (pass16,da15)
<HPT DISK 0_16 4.00> at scbus5 target 16 lun 0 (pass17,da16)
<HPT DISK 0_17 4.00> at scbus5 target 17 lun 0 (pass18,da17)
<HPT DISK 0_18 4.00> at scbus5 target 18 lun 0 (pass19,da18)
<HPT DISK 0_19 4.00> at scbus5 target 19 lun 0 (pass20,da19)
<HPT DISK 0_20 4.00> at scbus5 target 20 lun 0 (pass21,da20)
<HPT DISK 0_21 4.00> at scbus5 target 21 lun 0 (pass22,da21)
<HPT DISK 0_22 4.00> at scbus5 target 22 lun 0 (pass23,da22)
hpt_disk_1/15/1 is the same as <HPT DISK 0_15 4.00> , and is therefore da15 which is a 3tb WD with a serial no WMATV4761212
root@constellation:~ # camcontrol devlist
<DOGFISH 30G Q0707A> at scbus1 target 0 lun 0 (pass0,ada0)
<HPT DISK 0_0 4.00> at scbus5 target 0 lun 0 (pass1,da0)
<HPT DISK 0_1 4.00> at scbus5 target 1 lun 0 (pass2,da1)
<HPT DISK 0_2 4.00> at scbus5 target 2 lun 0 (pass3,da2)
<HPT DISK 0_3 4.00> at scbus5 target 3 lun 0 (pass4,da3)
<HPT DISK 0_4 4.00> at scbus5 target 4 lun 0 (pass5,da4)
<HPT DISK 0_5 4.00> at scbus5 target 5 lun 0 (pass6,da5)
<HPT DISK 0_6 4.00> at scbus5 target 6 lun 0 (pass7,da6)
<HPT DISK 0_7 4.00> at scbus5 target 7 lun 0 (pass8,da7)
<HPT DISK 0_8 4.00> at scbus5 target 8 lun 0 (pass9,da8)
<HPT DISK 0_9 4.00> at scbus5 target 9 lun 0 (pass10,da9)
<HPT DISK 0_10 4.00> at scbus5 target 10 lun 0 (pass11,da10)
<HPT DISK 0_11 4.00> at scbus5 target 11 lun 0 (pass12,da11)
<HPT DISK 0_12 4.00> at scbus5 target 12 lun 0 (pass13,da12)
<HPT DISK 0_13 4.00> at scbus5 target 13 lun 0 (pass14,da13)
<HPT DISK 0_14 4.00> at scbus5 target 14 lun 0 (pass15,da14)
<HPT DISK 0_15 4.00> at scbus5 target 15 lun 0 (pass16,da15)
<HPT DISK 0_16 4.00> at scbus5 target 16 lun 0 (pass17,da16)
<HPT DISK 0_17 4.00> at scbus5 target 17 lun 0 (pass18,da17)
<HPT DISK 0_18 4.00> at scbus5 target 18 lun 0 (pass19,da18)
<HPT DISK 0_19 4.00> at scbus5 target 19 lun 0 (pass20,da19)
<HPT DISK 0_20 4.00> at scbus5 target 20 lun 0 (pass21,da20)
<HPT DISK 0_21 4.00> at scbus5 target 21 lun 0 (pass22,da21)
<HPT DISK 0_22 4.00> at scbus5 target 22 lun 0 (pass23,da22)