Anyone knows what's the meaning of this error on log?
Apr 20 20:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 20:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 20:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 20:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 21:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 21:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 21:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 21:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 20:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 20:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 20:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 20:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 21:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 21:10:51 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors
Apr 20 21:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Currently unreadable (pending) sectors
Apr 20 21:40:52 freenas smartd[2598]: Device: /dev/ada4, 17 Offline uncorrectable sectors