If you are configuring a HyperSwap® system
that uses Fibre Channel connections, ensure that all SAN and Fibre Channel-specific requirements are
met.
You must configure a
HyperSwap
system to meet the following requirements:
- Directly connect each node to two or more SAN fabrics at the primary and secondary sites (2 - 8
fabrics are supported). Sites are defined as independent failure domains. A failure domain is a part
of the system within a boundary. Any failure within that boundary (such as a power failure, fire, or
flood) is contained within the boundary. The failure affects any part that is outside of that
boundary. Failure domains can be in the same room or across rooms in the data center, buildings on
the same campus, or buildings in different towns. Different kinds of failure domains protect against
different types of faults.
- Connections can vary based on fibre type and small form-factor pluggable (SFP) transceiver (longwave and shortwave).
- Nodes that have connections to switches that are longer than 100 meters (109 yards) must use
longwave Fibre Channel connections. A longwave small form-factor pluggable (SFP) transceiver can be purchased as an optional
component, and must be one of the longwave SFP transceivers that are listed at the following
website:
www.ibm.com/support
- Avoid using inter-switch links (ISLs) in paths between nodes and external storage systems. If
this configuration is unavoidable, do not oversubscribe the ISLs because of substantial Fibre
Channel traffic across the ISLs. For most configurations, trunking is required. Because ISL problems
are difficult to diagnose, switch-port error statistics must be collected and regularly monitored to
detect failures.
- Using a single switch at the third site can lead to the creation of a single fabric rather than
two independent and redundant fabrics. A single fabric is an unsupported configuration.
- Ethernet port 1 on every node must be connected to the same subnet or subnets. Ethernet port 2
(if used) of every node must be connected to the same subnet (this might be a different subnet from
port 1). The same principle applies to other Ethernet ports.
- Some service actions require physical access to all nodes in a system. If nodes in a HyperSwap system are separated by more
than 100 meters, service actions might require multiple service personnel. Contact your service
representative to inquire about multiple site support.
- Use consistency groups to manage the volumes that belong to an application. This structure
ensures that when a rolling disaster occurs, the out-of-date image is consistent and therefore
usable for that application.
- Use consistency groups to maintain data that is usable for disaster recovery for each
application. Add relationships for each volume for an application to an appropriate consistency
group.
- You can add relationships to a consistency group only in certain states, including both sites
accessible.
- If you need to add a volume to an application to provide it with more capacity at a time when
only one site is accessible, take careful note as you cannot create and add the HyperSwap relationship. Be sure to create
the relationship and add it to the group as soon as possible after the failed site is
recovered.
- If a storage system
is used at the third site, it must support extended quorum disks. More information is available in
the interoperability matrixes that are available at the following website:
www.ibm.com/support
- Place independent storage systems at the primary and secondary sites, and use active-active
relationships to mirror the host data between the two sites.
A HyperSwap system locates the
active quorum disk at a third site. If communication is lost between the primary and secondary
sites, the site with access to the active quorum disk continues to process transactions. If
communication is lost to the active quorum disk, an alternative quorum disk at another site can
become the active quorum disk.
A system of nodes can be configured to use up to three quorum disks. However, only one quorum
disk can be elected to resolve a situation where the system is partitioned into two sets of nodes of
equal size. The purpose of the other quorum disks is to provide redundancy if a quorum disk fails
before the system is partitioned.
Restriction: Do not connect an external storage system in one site directly to a switch
fabric in the other site.
An alternative configuration can use an extra Fibre Channel switch at the third site with
connections from that switch to the primary site and to the secondary site.
A HyperSwap system configuration is
supported only when the storage system that hosts the quorum disks supports extended quorum.
Although the system can use other types of storage systems for providing quorum disks, access to
these quorum disks is always through a single path.
For quorum disk configuration requirements, see the technote Guidance for Identifying and
Changing Managed Disks Assigned as Quorum Disk Candidates at http://www.ibm.com/support.