====== ZFS disc replace ======

===== faulty special device =====

Consider hddpool with special device as mirrors on 2 SSD partitions:

<code>
NAME                                              SIZE  ALLOC   FREE  CKPOINT  EXPANDSZ   FRAG    CAP  DEDUP    HEALTH  ALTROOT
hddpool                                          1.83T   294G  1.55T        -         -    22%    15%  1.00x  DEGRADED  -
  mirror-0                                       1.81T   291G  1.53T        -         -    22%  15.7%      -    ONLINE
    ata-TOSHIBA_HDWD120_81842ZHGS                1.82T      -      -        -         -      -      -      -    ONLINE
    ata-ST2000DM008-2FR102_WFL5BSR0              1.82T      -      -        -         -      -      -      -    ONLINE
special                                              -      -      -        -         -      -      -      -  -
  mirror-2                                         20G  2.94G  17.1G        -         -    30%  14.7%      -  DEGRADED
    ata-SSDPR-CX400-128-G2_GY2015459-part8       20.1G      -      -        -         -      -      -      -    ONLINE
    ata-SPCC_Solid_State_Disk_30041226481-part8  20.1G      -      -        -         -      -      -      -   FAULTED
</code>

to provide redundancy add any storage to special device ''mirror-2'' to turn it into 3-way mirror with one faulty device:
<code bash>
zfs create -V 21g nvmpool/special
zpool attach hddpool ata-SPCC_Solid_State_Disk_30041226481-part8 /dev/zvol/nvmpool/special
</code>

Now it can wait for new disc.