Model 204 considerations

Model 204 takes advantage of Cache Fast Write (CFW).

Model 204 takes advantage of Cache Fast Write (CFW) for files CCASERV and CCATEMP if the DASD subsystem supports CFW, caching is active at the volume level, and you changed the default Model 204 CACHE parameter from X’00’.

If the update activity is enough for CFW to be called during a migration, TDMF stops the volume with error message GTD2363E – GTDIMON error due to the detection of a Cache Fast Write operation.

However, it is possible that during the life of a migration, the level of update activity does not warrant I/O operations to be run against the previously mentioned files. Subsequent to the swap of the volume, an I/O operation might be started to the files that use CFW, which causes the following Model 204 error messages to be created.

2163 – TROUBLE WITH DISK I/O ON FILE% C POST CODE = X’%X’ CSW X’%X’

2164 – TROUBLE WITH DISK I/O ON POST CODE = X’%X’ CSW X’%X’

These error messages are created because the Subsystem Identifier (SSID) for the target volume (new source) is different from the original source volume.

Set the Model 204 CACHE parameter to X’00’ before a TDMF migration. You must run a recycle of the Model 204 address space that might have a performance impact on the address space.

Notes:
  • If CFW is off at the subsystem level or if caching is off at the device level when Model 204 is started, this action is not necessary. For more information, see the Model 204 Command Reference Manual and the Model 204 Messages Manual.
  • Point-In-Time migrations are not stopped if CFW activity is detected.