z/VM: CP Commands and Utilities Reference - z/VM - IBM

DDR
If you know the density of the output tape, you can use the value for “BYTES
OUT” to calculate the approximate number of feet of tape used. The density is
dependent on the tape device and may be modified with the value for MODE on
the OUTPUT control statement.
The format of the tape depends on the type of the direct access volume.
Once the dump is complete, DDR writes a tape mark.
FTr
requests an output tape format of variable unblocked records with a maximum
size of 65535. Specifying FTR will reduce the number of read I/O operations
initiated on the device by reading many records (a full-track) for each operation.
In addition, the tape record format (variable length and unblocked) will result in
less tape used. The size of the records and the number of records on each
track written to the tape depends on the density of the tape. The option can be
used for those devices supporting the full-track-read feature (FTR): 3380, 3390
and for FBA devices. FTR is the default for the 3380 and 3390 and therefore
need not be specified.
If FTR is specified on the DUMP control statement for a count-key-data (CKD)
DASD but the control unit does not support the feature, a message is written,
and the operation proceeds with data written, in the old format.
For a count-key-data DASD, the data is moved cylinder by cylinder. Any number
of cylinders can be moved. The format of the resulting tape is:
v Non-FTR and Non-Compact Format:
Record 1: a volume header record, consisting of data describing the
volumes.
Record 2: a track header record, consisting of a list of count fields to restore
the track, and the number of data records written on tape. After the last count
field, the record contains key and data records to fill the 4 KB buffer.
Record 3: track data records, consisting of key and data records packed into
4 KB blocks, with the last record truncated.
Record 4: either the end-of-volume (EOV) or end-of-job (EOJ) trailer label.
The end-of-volume label contains the same information as the next volume
header record, except that the ID field contains EOV. The end-of-job trailer
label contains the same information as record 1, except that the cylinder
number field contains the disk address of the last record on tape and the ID
field contains EOJ.
v FTR or Compact Format:
Record 1 and Record 4 are the same as described for the non-FTR format.
Record 2: a track header record, consisting of fields containing the length of
the track, the density of the tape, and the number of count fields in the track
followed by the track contents.
Record 3: track data records, consisting of count-key-data records in 8 KB,
12 KB, or 48 KB blocks for 800, 1600, or 6250 BPI respectively. The last
block in all cases is a short block.
For FBA devices, the data is moved in sets of blocks. Each set is arbitrarily
called a track (there is no relation to device geometry in this terminology). Any
number of blocks can be moved with one DUMP statement. The format of the
resulting tape depends on whether the FTR option is used or not, and also on
the recording format of the tape.
v FBA Tape Format:
1804 z/VM: CP Commands and Utilities Reference