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284 DS8000 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 (PSF/RSD)
command to retrieve the information from the control unit. By doing this, there is no need to
maintain a table for this information.
13.2.4 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. For example, consider a situation
where 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.
13.2.5 DS8000 definition to host software
The DASD Unit Information Module (UIM) is changed to define the new control unit type of
2107. 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 2107 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 2107 control unit type will allow this storage facility to be uniquely
reflected in the Hardware Configuration Manager (HCM). The definition of the 2107 control
unit type in the HCD is not required to define an IBM 2107 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 255 per storage facility for the DS8000. The
number of devices per LSS is still limited to 256. The number of CKD logical volumes is
increased from 4K to 64K devices per storage facility.
13.2.6 Read control unit and device recognition for DS8000
The host system will inform the attached DS8000 of its capabilities, such that it supports
native DS8000 control unit and devices. The DS8000 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 commands now display device type 2107 in their output:
DEVSERV QDASD and PATHS command responses
IDCAMS LISTDATA COUNTS, DSTATUS, STATUS and IDCAMS SETCACHE
Figure 13-1 on page 285, displays output from the DEVSERV QDASD command, which
shows the device type as a 2107.