DB2 Space calculation – from pages to tracks

All system z DASD I/O systemsÂ base on the IBM DASD device type IBM 3390 Model 3 and are compatible to it. This means that all calculations a DB2 DBA or sysadm can to do are on basis of this type and model characteristics. Quite typical for this DASD model: 12 pages of DB2 data fit into 1 track. For older types, such as IBM 3380, which are not considered here, only 10 pages to fit into a track. More about DB2 data and storage, see below.
IBM Type 3390 Model 3
56664 bytes per track 849960 bytesÂ per cylinder 15 tracks perÂ cylinder 3339 cylinders per device	3339 cylinders x 15 trk/cyl = 50100 tracks/device	2838 MB/Device approx. 2.75 GB
DB2 space calcalution on basis ofÂ device type 3390
smallest unit DB2 can externalize: 1 page with 4 KB, Â which isÂ 4096 bytes	1 track = 56664 bytes overhead per block of records stored = 340 Bytes	56664 / (4096 + 340) = 12.773 which is 12 pagesÂ per track
12 pages = 12 x 4 KB = 48 KB net user data = 48 KB which claimÂ 55 KB space on DASD device DB2 data + 15% overhead = total usage ofÂ DASD storag	1 cylinder = 15 rracks x 12 pages = 180 pages = 720 KB	1 Device = 50100 tracks = 601200 pages = 2.4 GB DB2 net user data

16. Februar 2012 / DB2 for z/OS

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