[OpenAFS] Volume/file/cache size limits

[Jeffrey Hutzelman]

On Wed, 8 Aug 2001, Wim.Glassee wrote:

> Have there been any changes to the size limits for volumes, files and
> client disk caches since IBM's AFS version 3.6?
> 
> 8G/2G/700M will not be enough. I'm kind of dealing with large files and
> large throughput, so a 10G cache would suit me better.

Let's take these one at a time...

- The 8GB volume size limit is a figment of Transarc's imagination, and
  always has been.  You should be able to create arbitrarily larger
  volumes, but there are some issue to be aware of related to volume
  dumps and restores.  The first is that, depending on your operating
  system, you may not have anywhere to put a large volume dump file.
  And the second is that, as volumes get larger, you may approach the
  point where a volume dump/restore operation (including a move or
  release) may take longer than the volserver's timeout.  However, that
  problem does not seem to occur anywhere near 8GB on modern systems.

- The 2GB file size is due to a limitation in AFS data structures which
  represent file sizes and offsets.  There is no way to eliminate this
  limit without changes to the core fileserver protocol _and_ the volume
  dump format.  This is a useful idea, but don't expect to see it happen
  right away.

- I've never even _heard_ of a fixed cache size limit, of 700MB or
  anything else.  There certainly are reasons to limit the number of
  cache chunks to something reasonable, because of the way the cache
  management code works.  This limit basically varies with the size
  of your machine, and with patches to organize cache files in multiple
  directories, developers on the openafs-devel list have set up caches
  as large as 1GB with 300000 chunks.  This code isn't in the stable
  OpenAFS distribution yet, but I wouldn't be surprised to see it in the
  next release.

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