Logical copy and physical copy

The Create Image Copy function supports two process types; physical copy and logical copy.

Physical copy creates new data sets without changing the compression routine of the input image copy data set.

Logical copy can create a data set copy that has a compression algorithm different from the input data set. Logical copy is useful for comparing the compression ratio of two compression routines.

To create a logical copy of an image copy data set, specify CRCTYPE=L and COMP keyword in the ICEIN GLOBAL, GROUP, or CRC statement.

The Create Image Copy function automatically interprets the compression routine of input image copy data set. It expands the data, and then re-compresses it by the compression routine specified by the ICEIN CMPRTN keyword. Also it can be used to create a compressed image copy data set from a non-compressed image copy, or to create a non-compressed image copy data set from a compressed image copy.

The result of combining the input data set, COMP keyword, and the COMPRTN keyword is discussed in the following topics.

Subtopics:

Restrictions for creating logical copy

If one of the following conditions is met, the Create Image Copy function ignores CRCTYPE=L and applies physical copy:

  • The input image copy data set is created by the IMS Online Image Copy utility or the IMS IC2 utility.
  • The compression routine that was applied to the original image copy data set and the compression routine specified for the COMPRTN keyword are the same.
  • COMP=N is specified for the original image copy data set and it is not compressed.
CRCTYPE=L, which specifies to create a logical copy of the input image copy data set, is not supported if both of the following conditions are met:
  • The input image copy data set is created by the COPY process of Advanced Image Copy Services or the IMS Database Image Copy 2 utility (DFSUDMT0).
  • The original database data set is an encrypted database or is allocated as an extended format data set.

When creating more than one output data set from an original image copy data set, you cannot use different compression routines for each output data set.

Process type

When CRCTYPE=L is specified in the ICEIN control statement, the process type and the compressed format of the output data set are determined by the combination of the original image copy data set, the COMP keyword, and the COMPRTN keyword.

The following table shows the relationship between the compression type of image copy data set and output data set.

Table 1. Compression type and the output data set
Input image copy data set format COMP= COMPRTN= Output image copy data set
Type processed Format
Not compressed - - Physical copy Not compressed
N - Physical copy Not compressed
Y - Logical copy Compressed by FABJCMP1
Y FABJCMP1 Logical copy Compressed by FABJCMP1
Y FABJCMP2 Logical copy Compressed by FABJCMP2
Y FABJCMP3 Logical copy Compressed by FABJCMP3
Y FABJCMP4 Logical copy Compressed by FABJCMP4
Compressed by FABJCMP1 - - Physical copy Compressed by FABJCMP1
N - Logical copy Not compressed
Y - Physical copy Compressed by FABJCMP1
Y FABJCMP1 Physical copy Compressed by FABJCMP1
Y FABJCMP2 Logical copy Compressed by FABJCMP2
Y FABJCMP3 Logical copy Compressed by FABJCMP3
Y FABJCMP4 Logical copy Compressed by FABJCMP4
Compressed by FABJCMP2 - - Physical copy Compressed by FABJCMP2
N - Logical copy Not compressed
Y - Logical copy Compressed by FABJCMP1
Y FABJCMP1 Logical copy Compressed by FABJCMP1
Y FABJCMP2 Physical copy Compressed by FABJCMP2
Y FABJCMP3 Logical copy Compressed by FABJCMP3
Y FABJCMP4 Logical copy Compressed by FABJCMP4
Compressed by FABJCMP3 - - Physical copy Compressed by FABJCMP3
N - Logical copy Not compressed
Y - Logical copy Compressed by FABJCMP1
Y FABJCMP1 Logical copy Compressed by FABJCMP1
Y FABJCMP2 Logical copy Compressed by FABJCMP2
Y FABJCMP3 Physical copy Compressed by FABJCMP3
Y FABJCMP4 Logical copy Compressed by FABJCMP4
Compressed by FABJCMP4 - - Physical copy Compressed by FABJCMP4
N - Logical copy Not compressed
Y - Logical copy Compressed by FABJCMP1
Y FABJCMP1 Logical copy Compressed by FABJCMP1
Y FABJCMP2 Logical copy Compressed by FABJCMP2
Y FABJCMP3 Logical copy Compressed by FABJCMP3
Y FABJCMP4 Physical copy Compressed by FABJCMP4