ZFS checksum errors, when do I replace the drive?

Solution 1:

Having those errors across multiple drives seems to indicate a backplane/controller/cabling problem more than a disk or RAM issue.

Solution 2:

My general rule of thumb is that if the errors are continuing to rise unexpectedly, the disk needs replaced; if it's static, there might have been some transient condition that caused the error, and the system's not reproducing the conditions that caused problems.

A few checksum errors doesn't necessarily indicate anything bad mechanically with the drive (bit rot happens, ZFS just happens to detect it while other filesystems don't), but if those errors have happened over the course of an hour, then it's a much different situation than if they've happened over the course of a year.