The customer can decide when the cluster returns to an operational state from service if an automatic online (AONLINE) to supported z/OS LPARs is run. Then, the logical paths that are established from the system zLPAR that the cluster surfaced the unsolicited attention receive an unsolicited attention to request the zLPAR to vary the devices back online. Only z/OS LPARs support the CUIR function. Other IBM Z operating systems can exist and hold up service-prep until you manually vary off their devices. 

If the customer decides not to use AONLINE, the devices must be varied online again by using the MI. The original z/OS command ( Vary Online ) cannot be used to online the devices in the z/LPAR while in CUIR. The manual function (through the MI) must be used to online the drives that CUIR put offline. As of this writing, no option is available to bring online drives only partially (for example, to test a system) for quality assurance tests before the cluster is varied online to all systems again. 

Note:  If a device is varied offline for CUIR reasons and is unintentionally left in this state, the MVS VARY XXXX,RESET  command can be used to reset the device for CUIR reasons. This command should only be used if devices exist that are left in this state and should no longer be in this state. 

CUIR features the following limitations: 

GLYPH<SM590000> Can be enabled only when all clusters in grid are at R4.1.2 or later. 

GLYPH<SM590000> Only native LPARS with z/OS 2.2 or later and JES2 can use CUIR. Other setups can exist, but their devices must be manually varied offline and back online. 

GLYPH<SM590000> Only Service preparation/Service mode is supported. The CUIR function might be extended in the future. 

The following APARs must be installed: 

GLYPH<SM590000> OA52398 

GLYPH<SM590000> OA52390 

GLYPH<SM590000> OA52376 

GLYPH<SM590000> OA52379 

GLYPH<SM590000> OA52381 

New LI REQ  commands are provided to enable or disable CUIR and AONLINE and to get an overview of the current logical drive or path group information. The default is disabled. 

For more information, see IBM TS7700 Series Control Unit Initiated Reconfiguration (CUIR) User’s Guide , WP102743. 

## 2.5 Grid configuration examples 

Several grid configuration examples are provided in this section. These examples describe the requirements for high availability (HA) and DR planning. 

## 2.5.1 Homogeneous versus hybrid grid configuration 

Homogeneous configurations contain only TS7700Ds, TS7700Ts, or TS7700Cs. If you use an intermix of disk-only and tape-attached models, it is a hybrid configuration . Consider the information that is provided in this section when you choose whether a mixture of the types is best for you. 

