Volume group modes, Overview of volume group modes, Synchronous mode – HP 3PAR Operating System Software User Manual
Page 120: Overview of volume group modes synchronous mode
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To return the volume groups to the default policy and generate alerts for asynchronous periodic
resynchronizations that do not complete within the synchronization period, set the volume
groups to the over_per_alert policy by issuing either of the following commands:
# setrcopygroup pol over_per_alert
or:
# setrcopygroup pol over_per_alert -pat
Volume Group Modes
See the following:
For information about:
“Overview of Volume Group Modes” (page 120)
Comparison of the two types of modes
How remote-copy volume groups operate in synchronous
mode
“Asynchronous Periodic Mode” (page 121)
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 host write I/O response times may be longer
than in asynchronous periodic mode.
Asynchronous periodic mode volume groups resynchronize
periodically, either automatically or manually.
asynchronous periodic (in output: periodic)
Host I/O write response times 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, a host write must be committed
to both the primary and the backup storage systems before the primary array acknowledges the
host write (see
), as follows:
1.
The host sends a write request to the primary storage system.
2.
HP 3PAR Remote Copy writes the data to the caches of at least two nodes on the primary
system. This redundancy enables synchronization to continue if one node fails before the write
is replicated.
3.
Concurrently, HP 3PAR Remote Copy sends the write request through a communication link
to the backup system.
4.
HP 3PAR Remote Copy writes the replicated data to the caches on two nodes on the backup
storage system.
5.
HP 3PAR Remote Copy sends an acknowledgment that replication is complete from the backup
system to the primary system.
120 Working with Volume Groups