Diagnosis
The block characteristic is NOT in the aggregate, because the BLOCKSIZEis so small that no characteristic was found in the aggregate that hasenough instances to form enough blocks. As a consequence, the technicalcharacteristic CHANGEID is used to write "artificial" blocks into the Ftable of the aggregate. These then have to be compressed. If they arenot compressed, the read performance for this aggregate is reduced.
Try a larger value for BLOCKSIZE or change the aggregate definition sothat a smaller aggregate can also be used (clever use of the aggregatetree!).