Have worked with AIX for some years.  Not a REAL detail person on this
but basically my understanding is this:

1.  AIX doesn't "know" what your files are used for.

2.  As you have created a jfs filesystem, then the I/O has to go through it.
This includes any writes to files, regardless of whether file changes in size.
I forget the details but the jfs log keeps track of this and is used, for 
instance
in the case of sudden unorderly halt of your system.   I have had several
instances where the filesystem that had my storage pools failed to mount
on system reboot.  I had to run AIX command "fsck" on it first which,
for one  thing "replays the log".  (The OS filesystems automatically have
fsck run against them on system reboot, but non rootvg filesystems don't).

3.   It's the changing data that is kept up with by JFS.  (I guess it's roughly
like a redo log for Oracle, for a quick analogy).

Hope this helps.


David B. Longo
System Administrator
Health First, Inc.
3300 Fiske Blvd.
Rockledge, FL 32955-4305
PH      321.434.5536
Pager  321.634.8230
Fax:    321.434.5525
david.longo AT health-first DOT org


>>> Wanda.Prather AT JHUAPL DOT EDU 11/26/01 05:29PM >>>
That is something I am curious about, not being an AIX expert:

What is being logged to the JFS log that creates overhead in the TSM case?
I thought the JFS log was necessary because of changing files in the JFS
filesystem.
But TSM DB, LOG, and STGPOOL volumes (really files) are pre-formatted; their
size does not change.
So what is the JFS overhead when TSM is writing into those files?

Thanks!