====== copies=2 ======

For one HDD it is possible to write each data twice.
It can protect from:
  * bitrot
  * bad sector

<code bash>
zfs set copies=2 hddpool
</code>

[[https://docs.oracle.com/cd/E19253-01/819-5461/gevpg/index.html|Storing Multiple Copies of ZFS User Data]]