IBM i Series, Handbook

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iSeries Architecture: Fundamental Strength of the iSeries
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iSeries Architecture: Fundamental Strength of the iSeries
A properly designed switch disk cluster can offer advantages over a data replication cluster.
Because a switch disk cluster does not use data replication, there is less overhead on the
systems and, therefore, more resource available to process transactions. A switched disk
cluster can be simpler to operate. Domino 5.0.7 is the first application to take advantage of
this support and uses the switched disk architecture to attain ClusterProven specification.
Switched disks do not remove the requirement to have application resiliency. The application
is critical to the design of a true continuously available environment.
In this first release of Independent ASP, IFS files only are supported. For V5R1, IFS
applications such as Lotus Domino or many Web serving applications are supported. This is
useful in situations where workstations or communication lines are associated with the IFS
data and the associated application is being switched. Planning and setup work are required
to make sure the resources being switched are named identically on both servers.
Note: All I/O, not just the disk in the I/O tower, is switched. Any LAN, WAN, workstation
controllers, etc. in the I/O tower are switched at the same time.
Fibre Channel Adapters
With V5R1, the iSeries can attach external disk and tape subsystems via high speed fibre
channel disk and tape adapters. This enhances the iSeries’ ability to participate in Storage
Area Networks (SAN). Storage Area Networks (SANs) may be defined as a combination of
technologies – including hardware, software, and networking components – that provides
any-to-any interconnection of server and storage elements. Fibre Channel technology is often
used in many of the more flexible topologies and is gaining popularity and usage.
Without other components, a Fibre Channel cable runs directly from an iSeries Fibre Channel
adapter to a Fibre Channel adapter in a tape drive or IBM ESS (Shark). The cable can be up
to 500 meters long. If more than 500 meters is needed, a pair of hubs or switches is added to
the configuration, allowing up to 10,000 meters (10 km) distance. The iSeries supports a
specific managed hub. A managed hub is a hybrid, a limited switch, but smarter than a plain,
regular hub. The iSeries also supports a regular switch in QuickLoop mode.
Refer to “V5R1 System Unit Hardware (PCI)” on page 292 for information on the Fibre
channel adapters. See “Peripherals” on page 399 for information on hubs and switches. You
can refer to “Removable Storage Media Devices” on page 353 and “Removable Storage
Media Devices” on page 353 for tape drive information. For the IBM ESS, see “2105
Enterprise and Versatile Storage Servers” on page 393.