DoesNotExist
if (parent.DoesNotExist()
if (replacing.DoesNotExist() || child.IsResilvering()
if (isspare && !vd.IsSpare() && !replaced.DoesNotExist()) {
if (vd.DoesNotExist())
if (!replaced.DoesNotExist() && (replaced.IsResilvering() ||
if (vd.DoesNotExist())
bool DoesNotExist() const;