As far as I know there is no way to access it directly. I can think of a couple of reasons for his, yet one of the reasons is probably that the backups are so called hard-links, not necessarily files themselves. That is an important issue in the backup process of FMS12 as backups are created only if anything is changed, which is compared using the hard-linked-files. FileMaker urges users not to open or use the backup-files directly, but instead to copy the desired backup-file and use that copy. Otherwise the backup-process may get into problems.
An excellent explanation of the backup process can be found here: http://fmforums.com/forum/blog/13/entry-443-filemaker-server-12-backups-faqs/
I usually have either FTP access to the backups or use Remote Desktop. Even though I seldom need them, I want to be able to access them anytime if the need arises. Security-wise the access is restricted to the few machines I use as admin of the databases, which usually satisfies the IT-boys-and-girls. If they do give you a hard time about this, you might remember them kindly that they should facilitate your needs (ok, a along as they are reasonable, but in this case they definitely are) so you should be able to figure out a way which is acceptable for the both of you.
Having said all this, it would be nice if you could download a copy of a backup using the console. I have not had a look at FMS13 yet, maybe it has such a feature...
Thanks for this, Jan. Regarding the hard link thing, though, each back up file is a complete file, right?
No, it is not. Simply put it is something like this: a hard link is a reference to a file just as a shortcut/alias with the difference being that the entry in the directory table makes it look like a real file. (Google for more details) In effect this means that any program accessing the link sees a real file where it really is either an actual file or the location of the file referenced. A shortcut or alias only points to the file allowing you to open it, there is no moving/copying/deleting of the file. For example: assume that the database is unchanged. The first backup made will be an actual file. The second backup will be a hard link because nothing has changed, and writing a hard link takes far less time than writing a large database file. The third backup goes like this also. By now there is one actual backup file (the first) and two hard links each pointing to this file. The process is faster and takes less disk-space also.
Should you now open the file (changing timestamp and what not internally) all three backups will reflect these changes (as they all deal with the same file) and the backup system will be compromised. Whereas if you copy the second backup, your OS will actually copy the first backup ('real') file because the hard link points to that file. The file you copied is a 'real' file which you can alter any which way you want without disturbing the back up process, because it is not a part of it.
The above applies to the normal backup process of FMS12+, the incremental backup process works differently. Yet I would say that in general the basic is: never access a backup directly (or move them or anything), always copy a backup. Which seems like good advice anyway.
I hope this is somewhat clear, there is much to say on the backup process, I remember seeing an under-the-hood presentation of a FileMaker developer given on a devcon, which might be available via Technet, not sure.