Mirrored Ha Pairs - IBM N series Hardware Manual

Disks and disk shelf compatibility:
– Fibre Channel, SAS, and SATA storage are supported in standard HA pair
configuration if the two storage types are not mixed on the same loop.
– One node can have only Fibre Channel storage and the partner node can have only
SATA storage, if needed.
HA interconnect adapters and cables must be installed unless the system has two
controllers in the chassis and an internal interconnect.
Nodes must be attached to the same network and the network interface cards (NICs) must
be configured correctly.
The same system software, such as Common Internet File System (CIFS), Network File
System (NFS), or SyncMirror must be licensed and enabled on both nodes.
For an HA pair that uses third-party storage, both nodes in the pair must see the same
array LUNs. However, only the node that is the configured owner of a LUN has read and
write access to the LUN.
Tip: If a takeover occurs, the takeover node can provide only the functionality for the
licenses that are installed on it. If the takeover node does not have a license that was used
by the partner node to serve data, your HA pair configuration loses functionality at
takeover.
License requirements
The cluster failover (cf) license must be enabled on both nodes.

7.2.2 Mirrored HA pairs

Mirrored HA pairs have the following characteristics:
Mirrored HA pairs provide high availability through failover, as do standard HA pairs.
Mirrored HA pairs maintain two complete copies of all mirrored data. These copies are
called plexes, and are continually and synchronously updated when Data ONTAP writes to
a mirrored aggregate.
The plexes can be physically separated to protect against the loss of one set of disks or
array LUNs.
Mirrored HA pairs use SyncMirror.
Restriction: Mirrored HA pairs do not provide the capability to fail over to the partner node
if one node is lost. For this capability, use a MetroCluster.
Setup requirements and restrictions for mirrored HA pairs
The restrictions and requirements for mirrored HA pairs include those for a standard HA pair
with the following other requirements for disk pool assignments and cabling:
You must ensure that your disk pools are configured correctly:
– Disks or array LUNs in the same plex must be from the same pool, with those in the
opposite plex from the opposite pool.
– There must be sufficient spares in each pool to account for a disk or array LUN failure.
– Avoid having both plexes of a mirror on the same disk shelf because that configuration
results in a single point of failure.
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IBM System Storage N series Hardware Guide