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.

Related topic

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

Important

If you do not specify a device type, or you specify a type that is not in this table, the product uses a 3390 device type.

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.

On this page