ZFS Checksum errors without any Checksum errors?

[Zaphod Beeblebrox]

This bit confuses me.  The errors are on 'vr2' and 'raidz1-0' ... but not
on any of the disks.  I can let this complete and there's some 400 data
errors spread all around, but the disks will all read zero errors.  What do
errors on the array the the vdev mean, then?

How did I get here?  vr2-d2c (in my notation, dxy is the x'th drive in the
array, version y --- so d2c is the third time I've replaced d2) replaced
d2b... which is now refusing to spin up.  Stay away from 1.5T drives.
Anyways... If I let the resilver finish, it will finish without finding
errors on any particular drive --- but it will still report hundreds of
errors on vr2 (the array) and raidz1-0 (the 1st vdev).

        NAME               STATE     READ WRITE CKSUM
        vr2                ONLINE       0     0     7
          raidz1-0         ONLINE       0     0    14
            label/vr2-d0   ONLINE       0     0     0
            label/vr2-d1   ONLINE       0     0     0
            gpt/vr2-d2c    ONLINE       0     0     0  (resilvering)
            gpt/vr2-d3b    ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-d4a    ONLINE       0     0     0  block size: 512B
configured, 4096B native
            ada14          ONLINE       0     0     0
            label/vr2-d6   ONLINE       0     0     0
            label/vr2-d7c  ONLINE       0     0     0
            label/vr2-d8   ONLINE       0     0     0
          raidz1-1         ONLINE       0     0     0
            gpt/vr2-e0     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e1     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e2     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e3     ONLINE       0     0     0
            gpt/vr2-e4     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e5     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e6     ONLINE       0     0     0  block size: 512B
configured, 4096B native
            gpt/vr2-e7     ONLINE       0     0     0  block size: 512B
configured, 4096B native
        logs
          gpt/vr2log       ONLINE       0     0     0
        cache
          gpt/vr2cache     ONLINE       0     0     0

errors: 427 data errors, use '-v' for a list