[OpenAFS] Defining size of AFS client disk cache

[Wheeler, JF (Jonathan)]

I thought I understood the rules for defining the size of the disk cache for
an AFS client, in that the third parameter of the file
/usr/vice/etc/cacheinfo should be no more than 90% of the size of the disk
partition user for the cache.  For a particular Linux client running OpenAFS
version 1.11, I have:

[csflnx61] $ cat /usr/vice/etc/cacheinfo 
/afs:/usr/vice/cache:100000
[csflnx61] $ df -k /usr/vice/cache
Filesystem           1k-blocks      Used Available Use% Mounted on
/dev/hda6               116648     95031     15595  86% /afscache
[csflnx61] $ fs getcacheparms
AFS using 88916 of the cache's available 100000 1K byte blocks.

Note that 100000/1166.48 = 85.7 %.  Yet a user copying several large files
from AFS into a Unix partition or running md5sum -c on those files generates
input/output errors at random points (i.e. the errors nearly always occur,
but not at the same point).  Reducing the size of the available cache by
issuing the command (as root);

fs setcachesize 90000

allows either of the commands above to complete successfully.

Note that the files involved consist of approximately 850 Mb of data.  Any
comments would be welcome.  The system where the error was first seen is a
multi-user system, so it is important to get the configuration right; this
is the fist time we have seen his sort of problem for some time (previously
it was also the available cache size which was wrong).

Jonathan Wheeler
e-Science Centre
Rutherford Appleton Laboratory