Large File Data Set (LFDS)
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Overview
When TurboIMAGE was introduced, the size of a data set was limited to 4GB (this was the MPE limitation until recently). When users demanded a larger data set, JUMBO data set was introduced, which can have a maximum size of 396GB (max. size per chunk multiplied by max. no. of chunks = 4GB * 99 = 396GB). Jumbo and single file data set are functionally similar except for dynamic expansion capability; while single file data set can grow dynamically, jumbo data set cannot. Now, with the availability of LARGE FILES (file greater than 4GB) on MPE, starting from version 6.5, we can increase the limit on a single file data set to 128GB, which is now the MPE file system limit.
Changes
- Creation of Large File Data Set
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.
NOTE: Large File Data Set cannot co-exist with Jumbo data set within one database. For example, a database contains either all single file data sets if their size are less than 128GB or if any of a data set is greater than 128GB in size, all the data sets that their size are greater than 4GB have to be Jumbo data set. However, TurboIMAGE supports both LFDS and Jumbo. - DBUTIL DBUTIL "show all" command displays the current usage of data set file. Depending on whether or not the database has large file data sets, either Database has at least one large file dataset or Database has no large file dataset present is displayed.
- DBINFO DBINFO mode 406 returns information about fully qualified database name and open mode. In addition to that, the 17th element is a bitmap denoting which features this database has used. If the 8th bit (start from left, 0 based) is 1, it denotes the database has at least one large file data set, otherwise it is 0.
Conversion
The customer can convert Jumbo data set to Large File data set by using DBLOAD/DBUNLOAD utility. DBLOAD/DBUNLOAD has been enhanced to unload database to one or more disk files instead of writing to tape. Third party tools are available for this kind of conversion if performance is the concern.
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