A mechanism must exist to allow this sharing of resources in a seamless way. This mechanism is called the hypervisor.

The hypervisor provides the following capabilities:

￿Reserved memory partitions allow the setting aside of a certain portion of memory to use as cache and a certain portion to use as NVS.

￿Preserved memory support allows the contents of the NVS and cache memory areas to be protected in the event of a server reboot.

￿The sharing of I/O enclosures and I/O slots between LPARs within one storage image.

￿I/O enclosure initialization control so that when one server is being initialized it doesn’t initialize an I/O adapter that is in use by another server.

￿Memory block transfer between LPARs to allow messaging.

￿Shared memory space between I/O adapters and LPARs to allow messaging.

￿The ability of an LPAR to power off an I/O adapter slot or enclosure or force the reboot of another LPAR.

￿Automatic reboot of a frozen LPAR or hypervisor.

4.3.1RIO-G - a self-healing interconnect

The RIO-G interconnect is also commonly called RIO-2. Each RIO-G port can operate at 1 GHz in bidirectional mode and is capable of passing data in each direction on each cycle of the port. This creates a redundant high-speed interconnect that allows servers on either storage complex to access resources on any RIO-G loop. If the resource is not accessible from one server, requests can be routed to the other server to be sent out on an alternate RIO-G port.

4.3.2 I/O enclosure

The DS8000 I/O enclosures use hot-swap PCI-X adapters These adapters are in blind-swap hot-plug cassettes, which allow them to be replaced concurrently. Each slot can be independently powered off for concurrent replacement of a failed adapter, installation of a new adapter, or removal of an old one.

In addition, each I/O enclosure has N+1 power and cooling in the form of two power supplies with integrated fans. The power supplies can be concurrently replaced and a single power supply is capable of supplying DC power to an I/O drawer.

4.4 Server RAS

The DS8000 design is built upon IBM’s highly redundant storage architecture. It also has the benefit of more than five years of ESS 2105 development. The DS8000 thus employs similar methodology to the ESS to provide data integrity when performing write operations and server failover.

4.4.1 Metadata checks

When application data enters the DS8000, special codes or metadata, also known as redundancy checks, are appended to that data. This metadata remains associated with the application data as it is transferred throughout the DS8000. The metadata is checked by various internal components to validate the integrity of the data as it moves throughout the

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IBM DS8000 manual Server RAS, RIO-G a self-healing interconnect, 2 I/O enclosure, Metadata checks