IBM DS6000 - Manual (Page 228)

204 IBM System Storage DS6000 Series: Copy Services with IBM System z
You can also request that a pair be suspended as soon as it reaches the full-duplex state
(see go to sync and suspend in Figure 17-2).
Pairs cannot change directly from full duplex state to copy pending state. They must go
through an intermediate suspend state.
You can go from suspended state to copy pending state during an incremental copy
(copying out-of-sync tracks only). This process is similar to the traditional transition from
suspended state to full duplex state (see the Resync arrow in Figure 17-2 on page 203).
17.3 Global Copy positioning
Figure 17-3 lists the main points for considering Global Copy.
Figure 17-3 Global Copy positioning
As summarized in Figure 17-3, Global Copy is a recommended solution when you want to
perform remote data copy, data migration, offsite backup, and transmission of inactive
database logs without impacting application performance, which is particularly relevant when
implemented over continental distances. Global Copy can also be used for application
recovery solutions based on periodic point-in-time copies of the data. This requires short
quiescings of the application’s I/O activity.
It can be used over continental distances with excellent application performance
The distances only limited by the network and channel extenders capabilities
Application write operations do not have synchronous-like overheads
Fuzzy copy of data at the recovery site (sequence of dependent writes may not be
respected at the recovery site)
Recovery data can become a consistent point-in-time copy of the primary data, if
appropiate application checkpoints are set to do global catch-ups
Pairs are synchronized with application group consistency
Synchronizations can be done more frequently, because of short catch-ups
RPO still not zero, but improves substantially
Global Copy is a recommended solution for remote data copy, data Global Copy is a recommended solution for remote data copy, data
migration and offsite backup - over continental distances without migration and offsite backup - over continental distances without
impacting application performance. impacting application performance.
It can be used for application recovery implementations if application I/O It can be used for application recovery implementations if application I/O
activity can be quiesced and non-zero data loss RPO is admissible. activity can be quiesced and non-zero data loss RPO is admissible.