Building Disaster Recovery Serviceguard Solutions Using Metrocluster with Continuous Access EVA P6000 for Linux B.01.00.00

shutdown of the system before the redundant system takes over. An unplanned failover occurs
when a failure or outage occurs that may not allow an orderly transition of roles.
NOTE: Failover can take other forms:
• Controller failover — The process that occurs when one controller in a pair assumes the
workload of a failed or redirected controller in the same array.
• Fabric or path failover — I/O operations transfer from one fabric or path to another.
Failsafe mode
Failsafe mode is only available when a DR group is being replicated in synchronous mode and
specifies how host I/O is handled if data cannot be replicated between the source and destination
array. The failsafe mode can be one of the following:
• Failsafe enabled — All host I/O to the DR group is stopped if data cannot be replicated
between the source array and destination array. This ensures that both arrays will always
contain the same data (RPO of zero). A failsafe-enabled DR group can be in one of two states:
◦ Locked (failsafe-locked) — Host I/O and remote replication have stopped because data
cannot be replicated between the source and destination array.
◦ Unlocked (failsafe-unlocked) — Host I/O and remote replication have resumed once
replication between the arrays is re-established.
• Failsafe disabled — If replication of data between the source and destination array is
interrupted, the host continues writes to the source array, but all remote replication to the
destination array stops and I/Os are put into the DR group write history log until remote
replication is re-established.
NOTE: Failsafe mode is available only in synchronous write mode. Host I/O can be recovered
by changing affected DR groups from failsafe-enabled mode to failsafe-disabled mode. This
action will begin logging of all incoming writes to the source member of the Data Replication
group.
Metrocluster with Continuous Access EVA P6000 for Linux does not support enabling Failsafe
Mode.
Failsafe on Link-down/Power-up
Failsafe on Link-down/Power-up is a setting that specifies whether or not virtual disks in a DR group
are automatically presented to hosts after a power-up (reboot) of the source array when the links
to the destination array are down and the DR group is not suspended. This prevents a situation
where the virtual disks in a DR group are presented to servers on the destination array following
a failover and then the virtual disks on the source array are also presented when it reboots. Values
for Failsafe on Link-down/Power-up are as follows:
• Enabled — Virtual disks in a source DR group are not automatically presented to hosts. This
is the default value assigned to a DR group when it is created. This behavior is called
presentation blocking and provides data protection under several circumstances. Host
presentation remains blocked until the destination array becomes available (and can
communicate with the source array) or until the DR group is suspended.
• Disabled — Virtual disks a source DR group are automatically presented to hosts after a
controller reboot.
NOTE: Metrocluster with Continuous Access EVA P6000 for Linux does not support enabling
Failsafe on Link-down/Power-up.
8 Introduction