I think ISO is seekable and from the sound of it, you want something to work on an OS where you have very little control over the utilities it offers (i.e. MS W

I think ISO is seekable and from the sound of it, you want something to work on an OS where you have very little control over the utilities it offers (i.e. MS Windows), where, I think ISO is supported by the pre-installed system utilities. The downside is that these aren't compressed. I don't think the OS that you chose gives you more options... it has native support for more filesystems, but using those as archives seems very problematic (but maybe I don't know something). Had you not been constrained by the choice of the operating system, a reasonable OS + FS combination will offer you some way to make snapshots. Filesystems are usually optimized for random access (with exception of things like TAR, which is designed for streaming). Most modern general purpose filesystems support compression, so that wouldn't be a problem. Often these filesystems offer a way to mount the file with the filesystem image w/o involving OS utilities like loop devices, so it would give you a way to access archive contents as if you were accessing any other filesystem.