The required size of the database directory depends on the maximums you established on the MAXPOOLS, MAXEXTNT, and MAXDBSPC parameters during database generation. The directory must be large enough to hold page table entries for the maximum size of the database. Figure 123 shows a formula for calculating the recommended size of a directory minidisk.
Figure 123. Formula for Calculating Directory Size (in Bytes)
Directory size = 7 558 + 16 x MAXDBSPC value
(in bytes) + 16 x MAXEXTNT value
+ 4 x MAXPOOLS value
+ 0.0021 x Maximum database size
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To estimate the value for the maximum database size, determine how many dbspaces (public, private, and internal) your database will need, and the number of pages needed by each dbspace; then multiply the total number of pages by 4096 to get the number of bytes. (You may want to overestimate this value to allow for creating unplanned dbspaces, and for increasing the number and size of internal dbspaces.) Finally, multiply this number by 0.0021, to determine how many bytes are needed in the directory to support these dbspaces. The result of this calculation includes the space needed for shadow paging.
Once you have the directory size, you can use the charts shown in the section Storage Capacities of IBM DASD Devices to determine the minidisk size specifications, in cylinders or blocks, of the device to be used.
| Note: | Although you do not have to specify the maximum database size during database generation, the size specified for the directory minidisk effectively establishes the limit. |