Read errors

For VSO areas, the first access to a CI causes it to be read from DASD and copied into the data space. From then on, all read requests are satisfied from the data space. If there is a read error from the data space, z/OS® abends.

For VSO areas that have been defined with the PRELOAD option, the data is preloaded into the data space; therefore, all read requests are satisfied from the data space.

To provide for additional availability, SHARELVL(2|3) VSO areas support multiple structures per area. If a read error occurs from one of the structures, the read is attempted from the second structure. If there is only one structure defined and a read error occurs, an AO status code is returned to the application.

There is a maximum of three read errors allowed from a structure. When the maximum is reached and there is only one structure defined, the area is stopped and the structure is disconnected.

When the maximum is reached and there are two structures defined, the structure in error is disconnected. The one remaining structure is used. If a write error to a structure occurs, the CI in error is deleted from the structure and written to DASD. The delete of the CI is done from the sharing partners. If none of the sharers can delete the CI from the structure, an EQE is generated and the CI is deactivated. A maximum of three write errors are allowed to a structure. If there are two structures defined and one of them reaches the maximum allowed, it is disconnected.