8464ch02_Architecture.fm Draft Document for Review February 7, 2020 3:15 pm Also, the function allows full read-write access to volumes that are assigned to a category that  is included in the exclusion list. The volumes that are assigned to the excluded categories can  be written to or have their attributes modified. In addition, those scratch categories that are  not excluded can optionally have their Fast Ready characteristics ignored, including Delete  Expire and hold processing. This configuration enables the DR test to mount volumes as  private that the production environment since returned to scratch (they are accessed as  read-only). One exception to the write protection is those volumes in the insert category. To enable a  volume to be moved from the insert category to a write protect-excluded category, the source  category of insert cannot be write-protected. Therefore, the insert category is always implied  to be a member of the excluded categories. Be sure that you have enough scratch space when Expire Hold processing is enabled to  prevent the reuse of production scratched volumes when you are planning for a DR test.  Suspending the volumes’ Return-to-Scratch proce ssing during the DR test is also advisable.  Because selective write protect is a cluster-wide function, separated DR drills can be  conducted simultaneously within one multi-cluster grid if each cluster has its own independent  client-configured settings.  For more information, see Chapter 14, “Disaster recovery testing” on page 769. This function builds upon the TS7700s ability to provide DR testing capabilities by introducing  FlashCopy consistency points within a DR location. A DR test host can use this DR family to  run a DR test while production continues on the remaining clusters of the grid.  For the DR host, the FlashCopy function provides data on a time consistent basis (Time  zero). The production data continues to replicate during the entire test. The same volumes  can be mounted at both sites at the same time, even with different data. To differentiate  between read-only production data at time zero and fully read/write-enabled content that is  created by the DR host, the selective write protect features must be used.  All access to write-protected volumes involves a snapshot from the time zero FlashCopy. Any  production volumes that are not yet replicated to the DR location at the time of the snapshot  cannot be accessed by the DR host, which mimics a true disaster. Through selective write protect, a DR host can create content to segregated volume ranges.  A total of 128 write exclusion categories supported, versus the previous 32 in R4.2 and prior.  Write protected media categories cannot be changed (by the DR host) while the Write  Protection mode is enabled. This fact is true for the data and the status of the volumes.  Therefore, it is not possible (by the DR host) to set production volumes from scratch to private  or vice versa. When the DR site has only TS7700Ds, the flash that is started during the DR  test is across all TS7700Ds in the configured DR-Family. As production returns logical  volumes to scratch, deletes them, or reuses them, the DR site holds on to the old version in  the flash instance in each cluster’s TVC. Theref ore, return to scratch processing can now run  at the production side during a test, and it does not need to deferred or expire hold used. The TS7700T or TS7700C can be a part of a DR Family, but the have some limitations for  those volumes that are not resident in disk cache at the time of the Flash.  94  IBM TS7700 Release 5.0 Guide 2.4.35 FlashCopy for DR testing 