||Oracle Tips by Burleson
Oracle10g Grid Computing
Chapter 12 - RAC Design Considerations
When a drive
fails, there must be an immediate spare available to replace it, even
if the hot spare is available. If the hot spare has already activated
and a second drive is lost, the entire array is in jeopardy. Most of
these arrays use hot-pluggable drives, meaning they can (in time of
failure) be replaced with the system running.
NICs and HBAs
While not shown in the diagram, every component
requires a connection to the others. This connection is usually via
a NIC (network interface card) or HBA (host bus adapter) interface.
These NIC or HBA interfaces should be the fastest possible,
especially in the case of the cluster interconnect and disk connect.
Failed NIC interfaces result in the loss of that component, unless a
second NIC card is immediately failed over to. A failure of the HBA
results in loss of connection to the disk array. At a minimum, a
spare NIC and HBA for each and every component must be available.
Wherever possible, use interchangeable NIC and HBA interfaces.
Provide Redundancy at
It is easy to see that redundancy at the
hardware level is vital. At each level of the hardware layout, an
alternate access path must be available. Duplicating all equipment
and configuring the automatic failover capabilities of the hardware
reduces the chances of failure to virtually nil. It is also critical
to have on-hand spares for non-redundant equipment such as NIC and
HBA cards and interface cables.
By providing the required levels of redundancy,
the system becomes highly available. Once there is an HA
configuration, it is up to the manager to plan any software or
application upgrades to further reduce application downtime. In
Oracle Database 10g using grid control, rolling upgrades are
supported, further increasing reliability. At the SAN level,
appropriate duplication software such as Veritas must be used to
ensure the SAN arrays are kept synchronous. Oracle Database 10g
allows for use of the Oracle Automatic Storage Management or ASM.
ASM allows for automated striping, backup and database flashback
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