74 IBM System Storage N series Hardware Guide
They own their spare disks, spare array LUNs (or both) and do not share them with the
other node.
They each have mailbox disks or array LUNs on the root volume:
– Two if it is an N series controller system (four if the root volume is mirrored by using the
SyncMirror feature).
– One if it is an N series gateway system (two if the root volume is mirrored by using the
SyncMirror feature).
They can be on the same Windows domain, or on separate domains.
7.1.3 Preferred practices for deploying an HA pair
To ensure that your HA pair is robust and operational, you must be familiar the following
guidelines:
Make sure that the controllers and disk shelves are on separate power supplies or grids so
that a single power outage does not affect both components.
Use virtual interfaces (VIFs) to provide redundancy and improve availability of network
communication.
Maintain a consistent configuration between the two nodes. An inconsistent configuration
is often the cause of failover problems.
Make sure that each node has sufficient resources to adequately support the workload of
both nodes during takeover mode.
Use the HA Configuration Checker to help ensure that failovers are successful.
If your system supports remote management by using a Remote LAN Management (RLM)
or Service Processor, ensure that you configure it properly.
Higher numbers of traditional volumes and FlexVols on your system can affect takeover
and giveback times.
When or FlexVols are added to an HA pair, consider testing the takeover and giveback
times to ensure that they fall within your requirements.
For systems that use disks, check for and remove any failed disks.
For more information about configuring an HA pair, see the Data ONTAP 8.0 7-Mode
High-Availability Configuration Guide, which is available at this website:
http://www.ibm.com/storage/support/nas
7.1.4 Comparison of HA pair types
Table 7-1 on page 75 lists the types of N series HA pair configurations and where each might
be applied.
Tip: The mailbox disks or LUNs are used to perform the following tasks:
Maintain consistency between the pair
Continually check whether the other node is running or it ran a takeover
Store configuration information that is not specific to any particular node
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