Content deleted Content added
Peter Flass (talk | contribs) →Specifying datasets: DCB acronym |
Peter Flass (talk | contribs) →Dataset integrity: link extent |
||
Line 9:
==Dataset integrity==
Normally, when a device is OPENed for EXCP, only the first "extent" is represented in the ''Data Extent Block'' (DEB). Among other information each DEB contains information on the ___location and size of each ''[[Extent (file systems)|extent]]'' of the data set. (Each DEB is forward- and backward-chained to the DCB as a system security measure as the DCB resides in unprotected user storage whereas the DEB resides in protected system storage, Subpool 253). If, for example, the programmer tries to read past the end of an extent, an exception occurs and the operation is suppressed, thereby preventing a data integrity exposure. Should the DEB include additional extents, the channel program may be updated by the programmer to refer to the next extent and the EXCP may be reissued, or the end of extent exit appendage, if provided, may update the channel program to the next extent and the operation may be re-driven without first going through the EXCP processor.
==Legacy datasets only==
| |||