> Dave, > How good of an idea is it to mount a filesystem R/O on a second Linux/390 > image? I would worry about problems due to Linux's aggressive use of > filesystem cache. Also, does CSE take care of the VM mini-disk caching > problem that I read about here? > > Thanks, > Folks, I apologize for not be more clear in my first note. While VM's CSE (Cross System extension) does allow for sharing physical DASD between two or more VM systems, it does not address the problem of mulitple guest operating systems (Linux or otherwise) accessing the same DASD in read/write mode at the same time. All CSE provides is the ability for each Linux (or CMS for that matter) guest, (one in each VM system) to access the same DASD at the same time. The first guest that accesses the DASD gets it in r/w mode, all other guests get it in r/o mode. This is controlled directly by CP itself, and uses a reserved area on the DASD to hold an access bit map of who has what accessed.
If the guest operating systems that physically share the DASD support a guest file system that understands how to handle simultaneous r/w access, then they can both read and write the same files at the same time on the shared DASD. However, since neither Linux's ext2fs nor CMS's minidisk file system know how to this, they can not reliably access the same files at the same time on the shared DASD. In other words, while the DASD can be physically shared, the file systems implemented on top of that DASD can not be. However, using CSE shared DASD is a good first step in setting up CMS and/or Linux services in a HA mode, for oblivious reasons. DJ
