One of my 6TB NAS drives just died. Not a big issue, as the harddrive is still in guarantee, and Western Digital has superb customer service. just fill out a form and you get a new disk, then send back the old one.
Of course your data should be encrypted in the first place 😀 you never know.

root@storage:~ # zpool offline storage /dev/gptid/feb58edc-34bb-11e2-8227-b8975a2ae4ef

root@storage:~ # zpool status storage

  pool: storage

 state: DEGRADED

status: One or more devices has been taken offline by the administrator.

Sufficient replicas exist for the pool to continue functioning in a

degraded state.

action: Online the device using ‘zpool online’ or replace the device with

‘zpool replace’.

  scan: resilvered 2.12T in 0 days 15:18:09 with 0 errors on Thu Jan 25 11:44:30 2018

config:

NAME                                            STATE     READ WRITE CKSUM

storage                                         DEGRADED     0     0     0

  raidz1-0                                      DEGRADED     0     0     0

    gptid/fdd627a8-34bb-11e2-8227-b8975a2ae4ef  ONLINE       0     0     0

    gptid/fe48d16c-34bb-11e2-8227-b8975a2ae4ef  ONLINE       0     0     0

    1956547944066614565                         OFFLINE      0     0     0  was /dev/gptid/feb58edc-34bb-11e2-8227-b8975a2ae4ef

    gptid/3158b989-013c-11e8-9491-001517d34dc1  ONLINE       0     0     0

root@storage:~ # gpart create -s gpt /dev/ada3

ada3 created

root@storage:~ # gpart add -b 128 -t freebsd-swap -s 2G /dev/ada3

ada3p1 added

root@storage:~ # gpart add -t freebsd-zfs /dev/ada3

ada3p2 added

root@storage:~ # gpart list ada3

Geom name: ada3

modified: false

state: OK

fwheads: 16

fwsectors: 63

last: 11721045127

first: 40

entries: 128

scheme: GPT

Providers:

1. Name: ada3p1

   Mediasize: 2147483648 (2.0G)

   Sectorsize: 512

   Stripesize: 4096

   Stripeoffset: 0

   Mode: r0w0e0

   rawuuid: f6f3c35f-01f8-11e8-9491-001517d34dc1

   rawtype: 516e7cb5-6ecf-11d6-8ff8-00022d09712b

   label: (null)

   length: 2147483648

   offset: 65536

   type: freebsd-swap

   index: 1

   end: 4194431

   start: 128

2. Name: ada3p2

   Mediasize: 5999027552256 (5.5T)

   Sectorsize: 512

   Stripesize: 4096

   Stripeoffset: 0

   Mode: r0w0e0

   rawuuid: fbe6c0a0-01f8-11e8-9491-001517d34dc1

   rawtype: 516e7cba-6ecf-11d6-8ff8-00022d09712b

   label: (null)

   length: 5999027552256

   offset: 2147549184

   type: freebsd-zfs

   index: 2

   end: 11721045119

   start: 4194432

Consumers:

1. Name: ada3

   Mediasize: 6001175126016 (5.5T)

   Sectorsize: 512

   Stripesize: 4096

   Stripeoffset: 0

   Mode: r0w0e0

root@storage:~ # zpool status storage

  pool: storage

 state: DEGRADED

status: One or more devices is currently being resilvered.  The pool will

continue to function, possibly in a degraded state.

action: Wait for the resilver to complete.

  scan: resilver in progress since Fri Jan 26 07:59:05 2018

8.80T scanned at 229M/s, 7.06T issued at 184M/s, 8.88T total

1.68T resilvered, 79.46% done, 0 days 02:53:18 to go

config:

NAME                                              STATE     READ WRITE CKSUM

storage                                           DEGRADED     0     0     0

  raidz1-0                                        DEGRADED     0     0     0

    gptid/fdd627a8-34bb-11e2-8227-b8975a2ae4ef    ONLINE       0     0     0

    replacing-1                                   OFFLINE      0     0     0

      16622126325015839303                        OFFLINE      0     0     0  was /dev/gptid/fe48d16c-34bb-11e2-8227-b8975a2ae4ef

      gptid/2d6266b8-0266-11e8-9491-001517d34dc1  ONLINE       0     0     0  (resilvering)

    gptid/fbe6c0a0-01f8-11e8-9491-001517d34dc1    ONLINE       0     0     0

    gptid/3158b989-013c-11e8-9491-001517d34dc1    ONLINE       0     0     0