It was likely written with one of the standard utilities, like tar or cpio. Try reading a table of contents with tar -tvf /dev/rmt/0 or cpio -ivBdumct </dev/rmt/0 (or without the "c" flag if you get "out of phase" messages). Neither of these will actually write the data. Remove the "t" flag in cpio to actually write the files, or with tar -xvf /dev/rmt/0. Maybe one of these will help.