You need to run a RTVDSKINF job then PRTDSKINF to view the disk space usage on your system.
This can run several hours though so run during downtime.
In the interim, do you schedule a cleanup job? CHGCLNUP F4 to view. If you haven’t then you can use this to cleanup your history logs, etc..
Or WRKOBJ OBJ(QSYS/QHST*) OBJTYPE(*FILE) to manually delete QHST files
Check the QRPLOBJ library, you can clear this library.
If you know your system, type wrkobj *all/*all *jrnrcv. Delete the excessive jrnrcvs.
WRKOBJPDM for a specific library and sort by object size or DSPLIB and print out to see the large objects.
RTVDSKINF/PRTDSKINF might be no help if you have no prior baseline or trend data. Further, it might be the cause of hitting the limit if you run it. RCLSTG should be avoided if you don’t know the cause — it won’t tell you anything.
V5R1?? or V6R1?
Sign on as an *ALLOBJ/*SPLCTL/*JOBCTL user at least.
Start a session and run WRKACTJOB. Press <F11> to view elapsed data. Place the cursor over in the column labeled AuxIO and press <F16> to sort. Start investigating the jobs from the top of the list on down. Press <F5> a couple times over the following couple of minutes to view refreshed statistics.
In a second session, run WRKOUTQ. (The default should be *ALL and you should have authority.) View the list to see if any *outq is receiving a high number of entries. Press <F5> to see if the number rises for any queue. Investigate suspicious *outqs to see what is being added.
I’d be suspicious of (1) journal receivers, (2) spooled files, (3) QRPLOBJ from a looping job and (4) streamfiles — it _might_ be a shared directory that’s getting added to. (RTVDIRINF/PRTDIRINF might be more appropriate than xxxDSKINF, but might also put you over the limit.)
If this is V6R1, it _might_ not be one of your jobs. If V6R1, is this a Power6 processor?