That should be DeviceMapper, not DataMapper.
An anonymous reader writes "The 2.8.2 release of DragonFly BSD is now available, featuring significant advances in multi-processor performance based on DragonFly's signature soft token locks. It also includes many feature advancements including: pf from OpenBSD 4.2, the Wifi stack from FreeBSD and DataMapper from NetBSD (with significant enhancements). This release also marks the return of the GUI image. See the release notes for full details."
If it is indeed a problem in practice, then it alone is plenty of reason.