[OpenAFS-devel] RE: fsck

[Jeffrey Hutzelman]

On Mon, 6 Nov 2000, Neulinger, Nathan R. wrote:

> What about the approach of the linux AFS server? It looks to me like it
> creates files in the directories on the system corresponding to AFS files.
> Why not just use this approach everywhere. It would certainly eliminate any
> of the issues with porting and supporting the server.

Because the directory lookup overhead on most UNIX filesystems is quite
high.  The result is that a server that accesses its data through links in
the filesystem is considerably slower than one that accesses them by inode
number.  IIRC, ext2 is better about this than most systems, but it's still
not as good as being able to do lookups by number.


Also, AFS keeps a small amount of metadata with each inode, namely the
parent volume, vnode, uniqifier, and data version of the vnode with which
that inode is associated.  This information can be of critical importance
when reconstructing a volume whose vnode indices were destroyed.  When the
through-the-filesystem approach is used, this metadata must be stored in
an index file somewhere else in the filesystem (possibly not even on the
same disk).  Storing it separately increases the chances that it will be
lost, or that the wrong data will be used.

-- Jeffrey T. Hutzelman (N3NHS) <jhutz+@cmu.edu>
   Sr. Research Systems Programmer
   School of Computer Science - Research Computing Facility
   Carnegie Mellon University - Pittsburgh, PA