TLMS VMF and IBM VLF.

Products

• TLMS Tape Management

Issue/Introduction

The client has a TLMS performance question, they want to know if they can add the TLMS.VMF dataset to VLF?

Cause

Any advantage using IBM VLF for the TLMS VMF.

Resolution

During the TLMS tape open and close process, TLMS issues a small read for the status of the volume or update the volume record during an OPEN output. These transactions are pretty small size wise and are very random. When running the TLMS daily scratch/movement(TLMSTRS), the entire VMF is read to determine what needs to be scratched and or moved.  Depending upon the size of the VMF, the job normally runs 10-30 mins.  Beyond that process, TLMS sits waiting for a tape mount to take place. 

IBM on VLF:

What kind of data objects does your application work with?

VLF works best with two kinds of data: (1) data objects that are members of partitioned data sets, located through a partitioned data set (PDS) concatenation, or (2) data objects that, while not PDS members, could be easily described as a collection of named objects that are repeatedly retrieved by many users. If neither description fits your data objects, it is likely that you would not obtain any performance benefit from VLF. 

How large are your data objects?

VLF works best with relatively small objects because less virtual storage is expended to reduce the number of I/O operations. Very large objects, if they are not used frequently enough to remain in central or expanded storage, might take longer to retrieve through VLF than through traditional I/O from DASD.


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"VLF works best with relatively small objects". Your TLMS VMF can run several 100 cylinders in size. This looks like a great feature from IBM, but I don't see TLMS as a decent candidate for it. Our file size is too large and the number of TLMS transactions processed every day would not justify the usage of the feature.