I think that part of the problem is that you have drive/volume expectations from Removeablefile devclass utilization, when in fact its a file-based mechanism. Two things you could do are to assure that the devclass MAXCAPacity value is sized that that it has the potential for writing a file as large as the capacity of your device (file system), and that your Unix resource limit "filesize" is not restricting the size. Also beware file size limits for a chosen file system type, which can be influenced by the block size chosen when the file system was initialized.
As you have noted, there's scant info about Removablefile devclass. I tried a search on the new Support page which alleges to replace the great TSM Support Page we once had - but the new Support page programming has severe defects, where it won't show more than 20 search results, despite 190 hits. (IBM's corporate self-delusion of replacing something that worked well for the customer base with something which satisfies corporate goals and nothing else.) Richard Sims