For CMS backups, DASDtapes require approximately 94-99 percent of the space occupied by the data that is actually backed up. Only the allocated areas of a minidisk are backed up. Data packing (compaction) can reduce the amount of space required to approximately 65-70 percent of the space occupied by the backed-up data. This figure can vary according to the type of data packed.
For physical backups, DASDtapes require approximately 110-115 percent of the space occupied by the backed-up data. The entire minidisk, including the unallocated areas, is backed up. Data packing can reduce the amount of space required to approximately 85-90 percent of the space occupied by the backed-up data. This figure can vary according to the type of data packed.
The size of the DASDtape file depends on the length of the tape to be simulated and the density at which the data is written. A 2400-foot DASDtape written at 6250 bpi occupies more space on a minidisk than a 2400-foot DASDtape written at 1600 bpi.
The following table lists estimates of the space required by DASDtape files written at varying densities.
|
DASD tape length (feet) |
Space required (approximate number of 4K blocks) when data is written at: |
||
|
1600 bpi |
6250 bpi |
38K bpi |
|
|
300 |
1,410 |
5,500 |
34,200 |
|
1,200 |
5,625 |
23,000 |
136,800 |
|
2,400 |
11,250 |
47,250 |
237,600 |
|
3,600 |
16,900 |
69,000 |
410,500 |
|
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