>> 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". 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. Regards, Saket Sinha -- 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>