On Wed 08-01-14 23:56:57, Saket Sinha wrote: > >> One of the big problems was that too many copyups were made on the > >> read-write file system. So we decided to implement an union file > >> system designed for diskless systems, with the following > >> functionalities: > >> > >> 1. union between only one read-only and one read-write file systems > >> > >> 2. if only the file metadata are modified, then do not > >> copy the whole file on the read-write files system but > >> only the metadata (stored with a file named as the file > >> itself prefixed by '.me.') > > So do you do anything special at CERN so that metadata is often modified > > without data being changed? Because there are only two operations where I > > can imagine this to be useful: > > 1) atime update - but you better turn atime off for unioned filesystem > > anyway. > > 2) xattr update > > > As already mentioned that the issue that we were facing was that "too > many copyups were made on the read-write file system". But my question is: In which cases specifically do you want to avoid copyups as compared to e.g. Overlayfs? > Writes to a file system in a unioning file system will produce many > duplicated blocks in memory since it uses a stackable filesystem > approach so response time for a particular operation is also a > concern. Honza -- Jan Kara <jack@xxxxxxx> SUSE Labs, CR -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>