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246 DS6000 Series: Concepts and Architecture
Today control unit single point of failure information is specified in a table and must be
updated for each new control unit. Instead, we can use the Read Availability Mask command
to retrieve the information from the control unit. By doing this, there is no need to maintain a
table for this information.
12.2.4 Initial Program Load (IPL) enhancements
During the IPL sequence the channel subsystem selects a channel path to read from the
SYSRES device. Certain types of I/O errors on a channel path will cause the IPL to fail even
though there are alternate channel paths which may work (or example, there is a bad switch
link on the first path but good links on the other paths). In this case, you cannot IPL since the
same faulty path is always chosen.
The channel subsystem and z/OS is enhanced to retry I/O over an alternate channel path.
This will circumvent IPL failures, due to the selection of the same faulty path to read from the
SYSRES device.
12.2.5 DS6000 definition to host software
The DASD Unit Information Module (UIM) is changed to define the new control unit type of
1750. The attachable device list will include 3380 and 3390 device types that include base
and alias Parallel Access Volumes (PAV). HCD users have the option to select 1750 as a
control unit type with 3380, 3380A, 3380B, 3390, 3390A, 3390B device types that can be
defined to this control unit.
The definition of the 1750 control unit type will allow this storage facility to be uniquely
reflected in the Hardware Configuration Manager (HCM). The definition of the 1750 control
unit type in the HCD is not required to define an IBM 1750 storage facility to z/Series hosts.
Existing IBM 2105 definitions could be used, but the number of LSSs will be limited to the
same number as today in the IBM 2105.
The number of LSSs is increased from 16 to 32 for the DS6000. The number of devices per
LSS is still limited to 256. The number of CKD logical volumes is increased from 4096 to 8192
devices per DS6000.
12.2.6 Read Control Unit and Device Recognition for DS6000
The host system will inform the attached DS6000 of its capabilities, such that it emulates a
DS8000. This does not limit any DS6000 functions. The DS6000 will then only return
information that is supported by the attached host system using the self-description data,
such as read data characteristics (RDC), sense ID, and read configuration data (RCD).
The following messages and command output display DS6000 information:
EREP messages
DEVSERV QDASD and PATHS command responses
The output from the IDCAMS LISTDATA COUNTS, DSTATUS, STATUS and IDCAMS will
display emulated DS8000s. The following DFSMS components and products are updated to
recognize real control unit and real device identifiers:
Device support - system initialization
DFSMSdss
System Data Mover (SDM)
Interactive Storage Management Facility (ISMF)