I notice that the dump command in NetBSD doesn't feature the use of any internal compression. If one compresses the dump file, then you can't use it as the basis for a restore.
Is that because the compression functions aren't in libc (ie.. they are off in libz or liblzma) ? Perhaps it's just a matter of someone doing the work ? It'd be a big help for admins who want to be able to use a modern compression algorithm without having to uncompress the dump to use it. I for one, would use it on all my systems. -Swift