Line cord

Fault indicator

indicators

 

EPO switch cover

Figure 2-2 Rack operator panel

You will note that there is not a power on/off switch on the operator panel. This is because power sequencing is managed via the S-HMC. This is to ensure that all data in non-volatile storage (known as modified data) is de-staged properly to disk prior to power down. It is thus not possible to shut down or power off the DS8000 from the operator panel (except in an emergency, with the EPO switch mentioned previously).

2.2 Architecture

Now that we have described the frames themselves, we use the rest of this chapter to explore the technical details of each of the components. The architecture that connects these components is pictured in Figure 2-3 on page 23.

In effect, the DS8000 consists of two processor complexes. Each processor complex has access to multiple host adapters to connect to channel, FICON, and ESCON hosts. Each DS8000 can potentially have up to 32 host adapters. To access the disk subsystem, each complex uses several four-port Fibre Channel arbitrated loop (FC-AL) device adapters. A DS8000 can potentially have up to sixteen of these adapters arranged into eight pairs. Each adapter connects the complex to two separate switched Fibre Channel networks. Each switched network attaches disk enclosures that each contain up to 16 disks. Each enclosure contains two 20-port Fibre Channel switches. Of these 20 ports, 16 are used to attach to the 16 disks in the enclosure and the remaining four are used to either interconnect with other enclosures or to the device adapters. Each disk is attached to both switches. Whenever the device adapter connects to a disk, it uses a switched connection to transfer data. This means that all data travels via the shortest possible path.

The attached hosts interact with software which is running on the complexes to access data on logical volumes. Each complex will host at least one instance of this software (which is called a server), which runs in a logical partition (an LPAR). The servers manage all read and write requests to the logical volumes on the disk arrays. During write requests, the servers

22DS8000 Series: Concepts and Architecture

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IBM DS8000 manual Architecture, Rack operator panel