Part 2 Challenge 9 used the ISMF, Interactive Storage Management Facility, panels which is a major disk administration tool. ISMF enables disk administrators to effectively manage the overall disk storage capacity for the enterprise.
Part 2 Challenge 10 explained "extents" where an "extent" is a contiguous area of disk space with an absolute beginning and ending location on disk. Each data set has 1 primary extent and optionally many secondary extents as needed. The disk VTOC, Volume Table of Content, keeps a record of all the extents on that disk volume.
A large enterprise z/OS environment can have thousands of disk volumes and thousands of tape volumes. Each disk volume and tape volume will have a unique volume label. These thousands of disk volumes and tape volumes are capable of storing millions of data sets.
While each disk and tape knows what data set names are contained on its own disk volume or tape volume, how can z/OS find a specific data set name among the thousands of volumes?
This challenge will provide that answer. This knowledge would begin to qualify you as a disk administrator candidate. If you are interviewed for large enterprise disk storage administrator position, the hiring authority would be impressed that you would have this knowledge.
What is the Master Catalog and what are User Catalogs?
The Master Catalog and User Catalogs is the short answer to "how can z/OS find a requested data set name among the thousands of volumes?"
However, the next question is, "how does the Master Catalog and User Catalogs manage to keep track of these thousands of disk volumes, tape volumes, and millions of data set names?
- From TSO/ISPF =6 panel , enter listc
- Observe your CC##### data sets were displayed
- Stating the obvious, which will become important later, is that all your data sets begin with CC#####
On your 3270 Emulator, locate the PA1 icon or keypad. PA1 is Attention, an interrupt, which is similar to cntl-c in Linux or Unix. If unable to locate PA1, then typically ESC or Alt-Ins will generate the PA1 signal. The next action you will take is going to create more output than you want to page through via the enter key to each '***'.
- From TSO/ISPF =6 panel , enter profile
- Observe the PREFIX value is set to your ID, CC#####
- From that same ISPF Command Shell panel, enter profile noprefix
- Now enter listc
- Yikes! What is all that. I entered the same listc command before with completely different results.
- PA1 icon, or ESC, or Alt-Ins to break out of the endless pages of stuff
- From that same ISPF Command Shell panel, enter profile prefix(cc#####)
- From that same ISPF Command Shell panel, enter profile and the prefix value should be your ID
- Now enter listc
- Back to normal
LISTC is short for List Catalog.
Things that z/OS technicians know about the Master Catalog and User Catalogs:
- Every z/OS has 1 and only 1 Master Catalog
- A single z/OS can have many User Catalogs
- Both the Master Catalog and the User Catalogs are VSAM data sets on disk volumes
- A Catalog has entries that associate a volume label with a data set name
- The Catalogs are seached for a requested data set name. A Catalog provides a volume label for the request to look in the VTOC of that volume label.
- When a new data set is created, a Catalog creates a new entry containing the data set name with the associated volume label where the data set was placed.
When LISTC was entered with PROFILE NOPREFIX, then the list catalog command started listing everything in the Master Catalog. The very first entry listed in the Master Catalog is the Master Catalog data set name.
When LISTC was entered with PROFILE PREFIX(CC#####), then the list catalog command started listing only catalog entries that begin with CC#####.
Best practices that are well known by experienced large enterprise Disk Administrators:
- Master Catalog stores critical operating data set names with associated disk volume label such as SYS1 data set names
- Master Catalog SHOULD NOT be used to keep track of business data set names
- User Catalogs should keep track of business data set names and the associated volume labels
- Master Catalog is searched first for business data set names
- Master Catalog stores "alias" entries which is effectively the data set name "prefix"
- Master Catalog "alias" entries include a related User Catalog name where the User Catalog has a catalog entry with the entire data set name with associated disk volume label
submit jcl(dsninfo) and review the output
This JCL that executes a series of system utility programs to gather CATALOG and VTOC details about a specific data set name might be something a disk administrator has in their personal JCL library toolbox.
A REXX routine was created to get specific data set name information displayed on the 3270 session immediately. A few errors exist in the REXX routine. Review of the JCL containing the system utility program control statements has the the challenge solution.
The REXX routine is taking only the most critical information to the you as a disk administrator. Specifically, only 2 of the 4 JCL steps are needed in the REXX routine, ALIAS and VTOCDSCB.
The objective is for the REXX routine to produce output from the DSNINFO JCL job ALIAS and VTOCDSCB steps. This is a total of 3 commands in the REXX routine that need minor alterations.
Edit CC#####.REXX.CLIST, then enter ex to left of member DSNINFO. This will execute the REXX routine that must be corrected to produce the same output as DSNINFO JCL job steps ALIAS and VTOCDSCB.
Use zos.public.hud.data.csv as the test case data set name input for the REXX routine.
Once satisfied with that REXX routine output, then submit 'zos.public.jcl(dsninfo)' . This JCL will write output from your REXX routine into P3.OUTPUT(#08)