Utility and Maintenance Functions › Enlarging the SCDS › Calculating SCDS Space Requirements

Calculating SCDS Space Requirements

We recommend that you monitor, from time to time, the number of free records within the SCDS. Each time a backup of the SCDS is run (see CASFBKUP), you get an audit trail report indicating the number of free blocks remaining. For more information, see Backing Up the SCDS earlier in this chapter.

If the free block value drops below 5 free blocks, CA SMF Director begins issuing warning messages whenever the SCDS is accessed. When less than 3 free blocks are present, this product terminates dump processing. Therefore, we recommend that you maintain a comfortable margin of free blocks.

In calculating the size of the SCDS file, it is helpful to understand the factors that affect its size. These are:

• The number of systems (SMF IDs) for which SMF history and inventory information.
• If recording SMF data to logstreams, the number of logstreams that each system is using for SMF recording.
• The number of history data sets.
• The number of magnetic tape volume serials to be defined for use by this product, and how long the SMF data is to be kept.

The SCDS consists of 4096 byte blocks with a minimum of at least 6 blocks needed for use by CA SMF Director. One and a half blocks are required for every 7 system configurations defined. If specific magnetic tape volumes are to be used by CA SMF Director, one block can contain 135 volume serials. These volumes are predefined to this product using the DUMPTAPES Control Statement (see the User Guide). If no volumes are defined, CA SMF Director requests a scratch tape (non-specific tape request) when a magnetic tape volume is needed.

The number of history data sets depends upon how frequently SMF dumps occur. Up to 30 data sets can be described per block, with one block required for every different year of SMF data retained.

The following formula can be used to calculate the number of blocks needed for the SCDS file:

  n1 = (c/4)
+ n2 = (v/135)
+ n3 = (((d * 365)/30)* y)* c
+ n4 = (cl * l) + (cs * (l + s)/4)
+ y
+ 6
________________________
z   Total number of SCDS blocks (note: round up fractional numbers)

where:

c

Number of different systems for which SMF data is to be retained.

v

Number of specific magnetic tape volumes to be defined.

d

Average number of SMF dump requests per day.

y

Number of years for which SMF data is to be kept.

cl

Number of systems that will be recording SMF data to logstreams.

l

Maximum number of logstreams that any system will be using to record SMF data.

cs

Number of systems that will be using any streams (logstreams or substreams).

s

Maximum number of substreams that any system will use.

Example:

    1 = (3/4)                         Three systems (remember to always round up)
+   0 = (0/135)                       No dedicated tapes (using DASD or SCRATCH)
+ 365 = (((2 * 365/30) * 5) * 3       Two dumps a day per system for 5 years
+   4 = (1 * 2) + (2 * (2 + 2)/4)     Three systems: one with 2 logstreams,
                                                     one with 2 substreams
+   5                                 Five years of SMF data
+   6                                 Six management blocks
______________________________________________________________________________
381                                   Total blocks needed