[OpenAFS] arla cachesize

Jeffrey Hutzelman jhutz@cmu.edu
Mon, 29 Dec 2003 14:15:23 -0500

On Tuesday, December 23, 2003 12:30:40 -0500 Derrick J Brashear 
<shadow@dementia.org> wrote:

> On Tue, 23 Dec 2003, amar deep kumar wrote:
>> Hi,
>>     what is the maximum cache size can be set with arla AFS client.
>> with " fs setcachesize" command i am only able to set cache size upto
>> 4GB. is there any limit. I want cache size upto 30GB.
> Perhaps you meant to ask the arla-drinkers mailing list?

Perhaps, but since the operation in question is done using a kernel 
interface shared between the two implementations, we can at least share 
what we know about that...

The argument to 'fs setcachesize' is passed to the kernel as a signed 
32-bit integer.  Thus, the largest value the interface can represent is
2147483647, which corresponds to a 2TB cache.

I see several places in the OpenAFS kernel code where the cache size is 
multiplied by a percentage.  The method used will certainly result in an 
overflow if the configured cache size is larger than about 1/100 of that 
number, or around 20GB.

Of course, I can't say whether Arla has the same or different limits.  I 
can certainly imagine ways in which limits at 2GB, 4GB, and 20GB could 
creep in...

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