Disk space or Swap space?
Which particular type of storage is it?
Does it have VPATHs?
Is it on EMC stuff?
There are quite a few things needed as info.
As a betting man, I am betting it is a compress volume on a storage system. Or files being compressed on the fly and uncompressing take a bit of IO saturation.
Other things could also be: preallocation of disk space, or cycling of files and not releasing the file until the daemon gets kicked. I saw an example of that on a Peoplesoft setup. The log was being compressed while the Daemon STILL had it open. When I found that and fixed the order of process, it sped up operations about 10 fold during busy times, wasn't any issue during low volume.
This was on an 8 processor AIX box with 16GB of memory. It hurt everytime.
On linux the proper command would be "lsof". On Solaris would be "truss", HPUX i am not sure.
If you wanna search locally try this:
man -k file | grep -i openshould get you close, to find the open files.
man -k open | grep -i file
apropos file | grep -i open
apropos open | grep -i file