One of the optimizations that databases with a schema and rotation disk use is to update a piece of data for a row. What this means is that no matter how large the object is, if the only update is a small piece, only that small piece will be updated, the rest of the data stays exactly where it is.
Because Aerospike does not have a schema, it is possible that the update may need more space and thus the record would have to be split or rewritten anyway. In addition, doing updates in-place on an SSD is likely to cause wear on the SSD and will quickly lead to hotspots. In the case of rotational disk this is not a problem, although rotational disk is much slower. In order to not suffer from these hotspot problems on SSDs, Aerospike employ a copy-on-write and will continually write to the SSD evenly.