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

Record 1: a volume header record, consisting of data describing the volume
Record 2: a track header record. This consists of data that describes the set
of blocks that follow (such as block numbers and the number of tape records
required to hold these FB-512 blocks). Following the control data are the
actual FB-512 blocks filling out the tape record. When possible, DDR will use
a 480K data buffer to store the FBA data (959 FBA blocks maximum). If
storage for this buffer cannot be obtained or if the OLDFORM option was
specified, then a smaller, 64K buffer will be used (127 FBA blocks maximum).
Record 3: FB-512 data records. These contain the rest of the blocks making
up the set. The record lengths of records 2 and 3 are 4K when FTR is not
specified. When FTR is specified, these tape records are 8K, 12K, or 48K
depending on the recording format of the tape.
Record 4: either the end-of-volume (EOV) or end-of-job (EOJ). 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 ID field
contains EOJ.
DDR
Note: When dumping with FTR to a 3490E or subsequent tape device, tape
records may vary in length (depending on the size of each track header
record) up to a maximum record length of 64K–1.
FTR32k
requests an output tape format of variable unblocked records with a maximum
size of 32654 bytes. Using this option instead of FTR will possibly result in
more I/O to the output device and is generally recommended only when an
output tape will be read by applications that cannot handle larger blocks.
Generally FTR (which is the default for many devices) is a better choice. See
FTR for a complete description of this option.
OLDFORM
indicates that the FBA data should be dumped using the smaller buffer (64K)
rather than the larger buffer (480K) to remain compatible with older versions of
DDR. The large buffer was implemented to enhance the performance of
dumping FBA data to a streaming tape drive in a virtual machine environment.
Using the OLDFORM option in this situation may degrade performance. This
option is ignored when dumping from a CKD/ECKD DASD.
COpy
requests that the utility copy data from one device to another device of the
same or equivalent type. Data may be recorded on a cylinder basis from input
device to output device. A tape-to-tape copy can be accomplished only with
data dumped by this program. A tape in compact format may be used as input.
For a tape-to-tape copy, the output is in the same format (compact, LZcompact,
or standard) as the input tape. The COMPACT or LZCOMPACT option on the
OUTPUT control statement is not valid for the COPY function. If it is specified,
a message stating COMPACT OPTION IGNORED FOR COPY OPERATIONS
is displayed.
REstore
requests that the utility return data that has been dumped by this program. Data
can be restored only to a DASD volume of the same or equivalent device type
from which it was dumped. It is possible to dump from a real disk and restore to
a minidisk as long as the device types are the same. A tape in a compact
format may be used as input. DDR checks to see if the input is in compact
format, and expands the data back to standard format, if needed. You do not
Chapter 3. CP Utilities 1805