Here’s something you never want to see: ZFS has detected a checksum error: eid: 138 class: checksum host: alexandria time: 2017-01-29 18:08:10-0600 vtype: disk This means there was a data error on the drive. But it’s worse than a typical data error — this is an error that was not detected by the hardware. Unlike most filesystems, ZFS and btrfs write a checksum with every block of data (both data a