HP Serviceguard Metrocluster manual Continuous Access EVA Link Suspend and Resume Modes

NOTE: Long delays in package startup time will occur in situations when recovering from broken pair affinity.

•The value of RUN_SCRIPT_TIMEOUT in the package ASCII file must be set to NO_TIMEOUT or to a large enough value to take into consideration the extra startup time required for getting status information from the P9000 and XP disk array. (See the earlier paragraph for more information on the extra startup time).

•Online cluster configuration changes might require a Raid Manager configuration file to be changed. Whenever the configuration file is changed, the Raid Manager instance must be stopped and restarted. The Raid Manager instance must be running before any Continentalclusters package movement occurs.

•A file system must not reside on more than one P9000 and XP frames for either the PVOL or the SVOL. An LVM Logical Volume (LV) must not reside on more than one P9000 and XP frames for either the PVOL or the SVOL.

•The application is responsible for data integrity, and must use the O_SYNC flag when ordering of I/Os is important. Most relational database products are examples of applications that ensure data integrity by using the O_SYNC flag.

•Each host must be connected to only the P9000 and XP disk array that contains either the PVOL or the SVOL. A given host must not be connected to both the PVOL and the SVOL of a Continuous Access pair.

Maintaining Metrocluster with Continuous Access EVA P6000 data replication environment

While the package is running, the package might halt because of unexpected conditions in the Continuous Access EVA volumes caused by a manual storage failover on Continuous Access EVA outside of Metrocluster Continuous Access EVA software. HP recommends that manual storage failover must not be performed while the package is running.

A manual change of Continuous Access EVA link state from suspend to resume is allowed to re-establish data replication while the package is running.

Continuous Access EVA Link Suspend and Resume Modes

Upon Continuous Access links recovery, Continuous Access EVA automatically normalizes (the Continuous Access EVA term for “synchronizes”) the source Vdisk and destination Vdisk data.

If the log disk is not full, when a Continuous Access connection is re-established, the contents of the log are written to the destination Vdisk to synchronize it with the source Vdisk. This process of writing the log contents, in the order that the writes occurred, is called merging. Since write ordering is maintained, the data on the destination Vdisk is consistent while merging is in progress.

If the log disk is full, when a Continuous Access connection is re-established, a full copy from the source Vdisk is done to the destination Vdisk. Since a full copy is done at the block level, the data on the destination Vdisk is not consistent until the copy completes.

If all Continuous Access links fail and if failsafe mode is disabled, the application package continues to run and writes new I/O to source Vdisk. The virtual log in EVA controller collects host write commands and data; DR group's log state changes from normal to logging. When a DR group is in a logging state, the log grows in proportion to the amount of write I/O being sent to the source Vdisks. If the links are down for a long time, the log disk might be full, and full copy happens automatically upon link recovery. If primary site fails while copy is in progress, the data in destination Vdisk is not consistent, and is not usable. To prevent this, after all the Continuous Access links fail, HP recommends manually setting the Continuous Access link state to suspend mode by using the Command View EVA UI. When Continuous Access link is in suspend state, Continuous Access EVA does not try to normalize the source and destination Vdisks upon links recovery until you manually change the link state to resume mode.

Maintaining the data replication environment 65