Hello Adrian, "Adrian Onsen": > 1. I don't quite understand what the "Copy-up" feature actually does, or how > it works. > > 2. I also don't understand what "white-outs" are. (It seems their > understanding is essential to understand the branch attribute option)
It is a basic feature of stacking filesystem. For example, - you have a cdrom which contains an entire linux system - you have an empty tmpfs - you mount an aufs with stacking tmpfs on the cdrom $ mount /dev/cdrom /cdrom $ mount -t tmpfs none /tmpfs $ mount -t aufs -o br:/tmpfs:/cdrom none /aufs - then you can see all files/directories on the cdrom from /aufs. additionally you can modify them under /aufs. - when you modify something /aufs, aufs will copy the file from cdrom to tmpfs automatically and apply the modifications to the file on tmpfs. - this behaviour is called Copy-on-Write (COW) or Copyup. - All the unmodified files are left on cdrom. /tmpfs has only the modified files. - if you want to remove a file, aufs creates a whiteout on tmpfs which is just a mark to hide the file on cdrom. > Can someone dumb these concepts down a little for me. Maybe with some > examples... The aufs man page is good, but maybe expects more knowledge then > I have. I'd suggest you to read documentats from Unionfs. It may be easier to understand a stackable filesystem, if you imagine a figure which shows one filesystem is stacking transparently over another fileysystem. Junjiro Okajima ------------------------------------------------------------------------- Sponsored by: SourceForge.net Community Choice Awards: VOTE NOW! Studies have shown that voting for your favorite open source project, along with a healthy diet, reduces your potential for chronic lameness and boredom. Vote Now at http://www.sourceforge.net/community/cca08
