Hp XP P9500 Storage User Manual download pdf (Page 148)

Problems that can occur

Journal data will not exist, and therefore the delta resync operation will fail, in the following cases:

• After creating the Cnt Ac-J pair, the primary delta resync P-VOL is updated but not the Cnt

Ac-J P-VOL.

• When the multi-target P-VOL is resynchronized after the Cnt Ac-S pair was split.

• When the Cnt Ac-J S-VOL is resynchronized after it was split.

• When the Cnt Ac-J pair is resynchronized after being split and then the journal volume at the

Cnt Ac-S secondary site exceeds 70 %.

• When the delta resync P-VOL is updated, and then the journal volume at the Cnt Ac-S secondary

site exceeds 70%.

• When the delta resync pair is created and no volumes (including volumes after failover or

failback) in the primary site are updated.

• When the status of the Cnt Ac-J pair for delta resync operation becomes HLDE, the journal

data necessary for the delta resync operation might be discarded. In this case, all data in the

delta resync P-VOL would be copied to the delta resync S-VOL.

Performing the delta resync operation

The delta resync operation is performed during disaster recovery. This operation copies differential

data from the Cnt Ac-S S-VOL to the Cnt Ac-J S-VOL.

The delta resync operation is part of the Pair Resync operation. Follow instructions in

“Resynchronizing pairs ” (page 60) to execute delta resync.

Assigning remote command devices

This section provides a workaround using remote command devices for the delta resync update

time-limit.

When the delta resync operation has been performed and pair status is changed to PAIR, the delta

resync P-VOL must be updated from the host for longer than five minutes. This is required to ensure

internal communications between the intermediate and remote sites.

However, you can work around this five-minute-plus update requirement by setting up command

devices and remote command devices. With remote command devices set up, communications

between the two sites is performed automatically, and the delta resync is ready to use when the

operation is run.

This requires setting up two command devices and two remote command devices on each site —

the local, intermediate, and remote sites — as explained in the following general guidelines.

Consult the HP XP P9000 External Storage for Open and Mainframe Systems User Guide for more

complete information about remote command devices.

1. Set up four command devices each on the local, intermediate, and remote sites.

2. Set up and dedicate two external ports and two target ports on each site for the

command/remote command devices. Configure paths between external ports and target ports.

For details about the external ports, see the HP XP P9000 External Storage for Open and

Mainframe Systems User Guide. For instructions on setting paths, see the HP XP P9000

Provisioning for Open Systems User Guide.

3. On each site, map a command device via a target port to a device on one of the other sites.

The device on the other site should be mapped to as a remote command device, using an

external port on that system.

4. Repeat the previous step so that two command devices on each site are mapped to a remote

command device on each of the other two sites.

148 Configurations with Continuous Access Synchronous

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