• Stefan Weinhuber's avatar
    [S390] dasd: add hyper PAV support to DASD device driver, part 1 · 8e09f215
    Stefan Weinhuber authored
    Parallel access volumes (PAV) is a storage server feature, that allows
    to start multiple channel programs on the same DASD in parallel. It
    defines alias devices which can be used as alternative paths to the
    same disk. With the old base PAV support we only needed rudimentary
    functionality in the DASD device driver. As the mapping between base
    and alias devices was static, we just had to export an identifier
    (uid) and could leave the combining of devices to external layers
    like a device mapper multipath.
    Now hyper PAV removes the requirement to dedicate alias devices to
    specific base devices. Instead each alias devices can be combined with
    multiple base device on a per request basis. This requires full
    support by the DASD device driver as now each channel program itself
    has to identify the target base device.
    The changes to the dasd device driver and the ECKD discipline are:
    - Separate subchannel device representation (dasd_device) from block
      device representation (dasd_block). Only base devices are block
      devices.
    - Gather information about base and alias devices and possible
      combinations.
    - For each request decide which dasd_device should be used (base or
      alias) and build specific channel program.
    - Support summary unit checks, which allow the storage server to
      upgrade / downgrade between base and hyper PAV at runtime (support
      is mandatory).
    Signed-off-by: default avatarStefan Weinhuber <wein@de.ibm.com>
    Signed-off-by: default avatarMartin Schwidefsky <schwidefsky@de.ibm.com>
    8e09f215
dasd_alias.c 25.8 KB