On Wed, 5 Dec 2001, Jim Doyle wrote: > > Does DFS take a huge performance hit due to its support of byte-level > > locking? > > Yes, there are a number of issues that come up with DCE/DFS. > > There is a token protocol between the fileserver and cache manager that > provides for exclusive rights, synchronized read-writes, etc. The token > meta-data is stored in memory in the fileserver instance and the > cache-mgr instance. DFS fileservers could possibly require very large > memory footprints in a big cell with frequent concurrent R/W access to > files. > > Another phenomenon with DFS is that when a file server crashes and > restarts, there is a "blackout" period in fileservice for some configured > period of time ; usually 15 minutes.. This period is called token state > recovery. During TSR, the file server sits and waits for cache managers > who had prior been issues tokens to file to contact it to renew their > tokens... This is how the fileserver rebuilds its list of clients locks > after crash, and re-estabilishes the precedence on granting range order > access to files... If a cache mgr is unable to reach the file server > following the crash (i.e. network outage) - that cache manager simply > becomes S.O.L. and simply loses whatever rights it held on access locks. > > Because the token protocol touches everything ; I doubt it would be > possible to make DFS work in disconnected mode operation. > > There is a white paper on the DFS token protocol out there - I belive it > was among the DCE 1.2.2 documentation tar ball. I havent touched DCE > stuff in years though ; and dont intend to ever again. :)
As Jim points out, the DFS token mechanism affects both performance and memory footprints, as well as makeing crash recovery take longer. It also has some unfortunate security effects -- in order to avoid excessive performance problems and some other nasty protocol problems, the DFS token protocol is completely unauthenticated. This means that any client can acquire a lock on absolutely anything at all, and keep that lock for as long as the server will let it (IIRC, that means forever, unless an administrator intervenes). -- Jeff _______________________________________________ OpenAFS-devel mailing list [EMAIL PROTECTED] https://lists.openafs.org/mailman/listinfo/openafs-devel
