Space estimation considerations
To estimate space requirements for Db2 objects, the Space Estimation facility relies on the following considerations:
- The maximum number of rows per page is 255.
- The maximum data set size for Db2 objects is as defined by PIECESIZE, DSSIZE, and the number of partitions.
- The maximum number of index pages per space map is 8,132.
- Db2 data pages are 4 KB, 8 KB, 16 KB, or 32 KB.
- A block is equivalent to a 4-KB page.
- All estimates are rounded up to nearest allocation unit boundary
- DASD device types and capacities are shown in the following table.
- If a Db2 object is allocated on multiple devices, space is estimated as though all devices are of the same type as that of the first extent.
DASD device types and capacities
Device type | Blocks/track | Tracks/cylinder | Blocks/cylinder |
|---|---|---|---|
3390 | 12 | 15 | 180 |
3380 | 10 | 15 | 150 |
The following table shows capacity of spacemaps for 4-KB, 8-KB, 16-KB, and 32-KB page sizes.
Spacemap capacities
Tablespace segment size | 4-KB page size pages/spacemap | 8-KB page size pages/spacemap | 16-KB page size pages/spacemap | 32-KB page size pages/spacemap |
|---|---|---|---|---|
0 (nonsegmented) | 10760 | 21680 | 43648 | 87216 |
0 (nonsegmented cluster member) | 199 | 199 | 199 | 199 |
4 | 1712 | 3436 | 6884 | 13784 |
8 | 2704 | 5440 | 10896 | 21824 |
12 | 3360 | 6744 | 13524 | 27084 |
16 | 3824 | 7680 | 15392 | 30800 |
20 | 4160 | 8360 | 16760 | 33560 |
24 | 4416 | 8904 | 17832 | 35712 |
28 | 4620 | 9324 | 18676 | 37408 |
32 | 4800 | 9664 | 19360 | 38784 |
36 | 4932 | 9936 | 19944 | 39924 |
40 | 5080 | 10200 | 20440 | 40920 |
44 | 5148 | 10384 | 20856 | 41712 |
48 | 5232 | 10560 | 21216 | 42432 |
52 | 5304 | 10712 | 21528 | 43056 |
56 | 5376 | 10864 | 21784 | 43624 |
60 | 5460 | 10980 | 22020 | 44100 |
64 | 5504 | 11072 | 22208 | 44544 |
For additional information about estimating DASD storage needs, refer to the Db2 documentation from IBM.
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