KB tracking

For each tape volume, the following data-related columns are tracked in the DB2 TAPEVOL table in kilobytes:

• The capacity of the tape volume
• The free space on the tape volume
• The number of logical bytes written to a tape volume
• The number of physical bytes written to a tape volume
• The number of logical bytes deleted from a tape volume

With larger capacity tapes, the possibility exists that these fields may overflow their signed 4-byte value. To handle this situation, five overflow-related columns (one for each of the columns above) now exist in the DB2 TAPEVOL table to account for the number of overflow KBs (in 2 GB increments). The overflow field will indicate the number of times the main 4-byte field has overflowed. The following example illustrates the logic that is implemented using the number of logical bytes written:

• A tape volume has 2147983647 KB logically written to it. This value is more than a signed 4-byte field will hold in KBs (which is 2147483647).
• Dividing the KB's written by 2 GB (2147483648) will result in the number of overflow KB's (in 2 GB increments) as well as the remainder resulting from the division. In this example, the overflow value will be 1 and the remainder from the division will be 499999:

  2147983647 / 2147483648 = 1 with a remainder of 499,999

• The main column in the DB2 TAPEVOL table that represents the amount of data logically written to the tape volume in KB will be 499999.
• To determine the amount of data on the tape volume (in KB), multiply the overflow value that is associated with the amount of data logically written to the tape volume by (2 GB) which is 2147983648 and then add the result of the multiplication to the value in the main field that represents the amount of KB logically written to the tape volume.
• The new overflow column that represents the number of 2 GB's written to the tape volume will be 1.