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ABCs of z/OS System Programming Volume 3 - IBM Redbooks

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8.7 ESS host adapters<br />

Host adapter bays<br />

4 bays<br />

4 host adapters per bay<br />

ESCON host adapters<br />

Up to 32 ESCON links<br />

2 ESCON links per host adapter<br />

2 Gb FICON host adapters<br />

Up to 16 FICON links<br />

1 FICON link per host adapter<br />

Auto speed detection - 1 Gb or 2 Gb<br />

SCSI host adapters<br />

Up to 32 SCSI bus connections<br />

2 SCSI ports per host adapter<br />

2 Gb Fibre Channel host adapters<br />

Up to 16 Fibre Channel links<br />

1 Fibre Channel port per host adapter<br />

Auto speed detection - 1 Gb or 2 Gb<br />

Figure 8-7 Host adapters<br />

ESS host adapters<br />

The ESS has four host adapter bays, two in each cluster. Each bay supports up to four host<br />

adapter cards. Each <strong>of</strong> these host adapter cards can be for FICON, ESCON, SCSI, or Fibre<br />

Channel server connection. Figure 8-7 lists the main characteristics <strong>of</strong> the ESS host<br />

adapters.<br />

Each host adapter can communicate with either cluster. To install a new host adapter card,<br />

the bay must be powered <strong>of</strong>f. For the highest path availability, it is important to spread the host<br />

connections across all the adapter bays. For example, if you have four ESCON links to a host,<br />

each connected to a separate bay, then the loss <strong>of</strong> a bay for upgrade only impacts one <strong>of</strong> the<br />

four connections to the server. The same is also valid for a host with FICON connections to<br />

the ESS.<br />

Similar considerations apply for servers connecting to the ESS by means <strong>of</strong> SCSI or Fibre<br />

Channel links. For open system servers, the Subsystem Device Driver (SDD) program that<br />

comes standard with the ESS can be installed on the connecting host servers to provide<br />

multiple paths or connections to handle errors (path failover) and balance the I/O load to the<br />

ESS.<br />

The ESS connects to a large number <strong>of</strong> servers, operating systems, host adapters, and SAN<br />

fabrics. A complete and current list is available at the following Web site:<br />

http://www.storage.ibm.com/hards<strong>of</strong>t/products/ess/supserver.htm<br />

Adapters can be intermixed<br />

Any combination <strong>of</strong> host<br />

adapter cards up to a<br />

maximum <strong>of</strong> 16<br />

Chapter 8. Storage management hardware 457

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