DFSMSsms, DFSMShsm, DFSMSdss, DFSMSdfp, ISMF. Any other storage related product installed at your site such as FAVER, IAM, CA-whatever ............. ad infinitum, and all of the associated pitfalls of each product. DFSMShsm has quite a few.
Also you need to be aware of trending to be able to estimate future DASD requirements, volume fragmentation, dataset fragmentation, VSAM reorganisations, VSAM key defined clusters.
And then of course there is the tape side of things, not quite so involved, but none the less daunting.
Well, that's most of the software out of the way, and that only leaves the hardware side ..........................