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Suprtool and LFDS

With the advent of MPE/IX 7.5 a new option for datasets greater than 4Gb became available in mid 2002 with Image version C.10.00. The option, called Large File Datasets (LFDS), puts all data into a single Large File if the data set size is greater than 4Gb. This was done with very little fanfare and basically flew in under the radar for most customers and even tool vendor providers such as Robelle.

LFDS became the new default for datasets over 4Gb. Previously, datasets that needed to be larger than 4Gb were implemented using "Jumbo datasets", a series of files built in the POSIX space in 4Gb chunks. Suprtool has supported Jumbo datasets for the last ten years, since they were created.

We started to look at how Suprtool would react to LFDS, but then reports came that there was corruption when using these datasets and that HP was re-visiting/fixing the code. Some months later we then heard that a new set of patches were being released in July/August 2005 timeframe and again started to look at the impact on Suprtool. However, we now have heard that there are new potential corruptions with the July/August 2005 set of patches and HP has again reviewed the design and implementation of LFDS.

Due to the previous corruption issues and that HP has the enhancement under review we cannot state that Suprtool supports this enhancement as yet. We will keep you posted on what we learn, but at this time we certainly would not recommend using LFDS.

You will get a LFDS if you specified a size thru Dbschema that was less than 128Gb. See the details below from HP's communicator article on this feature:

By default, any data set size less than 128GB is created as a single file data set, while a data set size greater than 128GB is created as Jumbo data set. The user can force creation of Jumbo data sets, if data set size is greater than 4GB, with a $CONTROL JUMBO option in the database schema. Each jumbo chunk file would be a maximum of 4GB and can have up to 99 chunks. If the user specifies $CONTROL NOJUMBO, which is default, any data set greater than 4GB but less than or equal to 128GB will be LFDS, while data set size greater than 128GB cannot be created.

We recommend that you always use $CONTROL JUMBO for all databases. Please not that LFDS cannot co-exist with Jumbo data sets within one database.

Adager is also capable of generating Large File datasets. However, you must set a special jcw in order for Adager to select this option over Jumbo datasets.

Adager also has a utility that will convert from Jumbo datasets to LFDS. However again, I personally would only use this for testing purposes and we are not endorsing that anyone use the LFDS feature in production.


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