XCOM for Linux 12.0 to z/OS transfers are slow for some files

Products

• XCOM Data Transport
• XCOM Data Transport - Linux PC
• XCOM Data Transport - z/OS

Issue/Introduction

Experiencing significant slowness with some daily XCOM jobs being transferred XCOM for Linux 12.0 to XCOM for z/OS 12.0.
The exact XCOM for Linux version is:
# xcomqm -r
xcomqm: CA XCOM Data Transport r12.0 23114 SP00 64bit (for <no SNA support>)

Environment

XCOM™ Data Transport® for UNIX/Linux 12.0
XCOM™ Data Transport® for z/OS 12.0

Resolution

From z/OS XCOMLOG files received it appears that record packing is not taking place i.e. incoming transfers show this message with no reference to BLOCKS:
XCOMM0147I xxxxxxxxxxxxxxxxxxx RECORDS RECEIVED

Record packing is very important for optimal transfer performance. It may be that other large files being transferred which do not see the same performance problem have some different structure and are not impacted as much by not using record packing. However generally it is advised to use to use record packing for all large file transfers.

The CARRIAGE_FLAG parameter is not being specified in the Linux xcomtcp transfer but it should default to the value XPACK per doc page: Reference > XCOM > Parameters CARRIAGE_FLAG.
However the XCOM for Linux version "r12.0 23114" being used contains a problem with the default value of CARRIAGE_FLAG not defaulting to XPACK.
This was fixed in patch LU15363 for level "r12.0 24110" ("Error XCOMU0492E with CARRIAGE_FLAG value of XPACK.") which also fixed another XPACK problem.
The latest patch LU15770 ("r12.0 25010") contains the same fix and it is advised to install that patch to resolve this problem.

NOTES:

• With the patch installed the CARRIAGE_FLAG parameter correctly defaults to XPACK (optimal record packing) and will not be necessary to add it as an extra parameter to the xcomtcp transfer.
  
  
• The MAXRECLEN is limited to 31744 to be able to use XPACK other wise this message will be seen
  XCOMU0484I Conflicting MAXRECLEN and CARRIAGE_FLAG parameters values. Setting CARRIAGE_FLAG value to YES for the transfer. 

Tests with LU15770 showed significant performance improvements and the z/OS XCOMLOG incoming transfers then showed expected use of record packing by reference to BLOCKS:
XCOMM0367I xxxxxxxxxxxxxxxxxxx BLOCKS yyyyyyyyyyyyyyyyyyy RECS RECEIVED