Image Jumbo Datasets

A pre-6.5 limit within the MPE file system is that no single me can be larger than 4GB. Many shops now have image datasets approaching that limit. In MPE/iX 5.5 (as well as a patch to MPE/iX 5.0) HP has introduced “Jumbo Datasets” to Image. Jumbos are datasets that can hold more than 4GB of data.

The method HP employs for implementing this is to break the dataset down into multiple files called “chunks.” These chunk files are stored as HFS files (sometimes called files in the POSIX namespace) each of which can be up to 4GB. The old dataset is just a control file with tables in it relating to the chunks.

The upside to this methodology is that Image internals control all of the file access, no program modifications are necessary and the datasets do not look any different to your applications. The downside is that your operational issues change because you have entered into the world of HFS files. Jumbo datasets will force you to use newer MPE command syntax to see hierarchical files (for example,: LISTF @.GROUP.ACCOUNT is replaced by : LISTFILE /ACCOUNT/GROUP/@).

The most important thing you must be absolutely certain of is that your system backup includes not only MPE named files but HFS files and directory structures as well. If it does not then you run the risk of losing the entire dataset.