HP 3PAR Operating System Software - Manual (Page 194)

28 Volume Group Modes
See: For information on:
“Overview of Volume Group Modes” (page 194) Comparison of the two types of modes
“Synchronous Mode” (page 194) How Remote Copy volume groups operate in synchronous
mode
“Asynchronous Periodic Mode” (page 195) How Remote Copy volume groups operate in asynchronous
periodic mode
Overview of Volume Group Modes
Description Volume Group Mode
Synchronous mode volume groups stay synchronized at
all times. synchronous (in output: sync)
Data integrity is greater than in asynchronous periodic
mode, but writes can take longer.
Asynchronous periodic mode volume groups resynchronize
periodically, either automatically or manually. asynchronous periodic (in output: periodic)
Writes can be faster than in synchronous mode, but data
is not always in sync.
Synchronous Mode
When Remote Copy volume groups operate in synchronous mode, the host initiates the write on
both the primary and the backup storage systems before the application acknowledges the host
write [
Figure 36 (page 195) ].
1. The host sends a write request to the primary storage system.
2. Remote Copy writes the data to the caches of at least two nodes on the primary system (up
to four if configured for RCIP). This redundancy enables synchronization to continue if one
node fails before the write is replicated.
3. Concurrently, Remote Copy sends the write request through a communication link to the backup
system.
4. Remote Copy writes the replicated data to the caches of at least two nodes on the backup
storage system.
5. Remote Copy sends an acknowledgement that replication is complete from the backup system
to the primary system.
194 Volume Group Modes