Defining use of zHyperLinks

You can specify whether data sets associated with this storage class are eligible to use zHyperLinks for reading and writing. zHyperLinks dramatically reduce latency by interconnecting the z14 Central processor complex directly to the I/O bays in the IBM® DS8880. This can improve application response time, without significant application changes.

Note: For the zHyperLink protocol to be enabled for I/O requests by the Db2® system, in addition to specifying a value of ENABLE, DATABASE, or ACTIVELOG for the ZHYPERLINK parameter, the SMS storage class of the Db2 data sets must be enabled for zHyperLink eligibility with the Integrated Storage Management Facility (ISMF).

zHyperLink technology is limited to 4 K CI for write, and the size specified in the current READLIMIT setting for read. When you specify ZHYPERLINK ENABLE or DATABASE option, zHyperLink read is enabled for Db2 objects with CI size less than or equal to the current READLIMIT setting. zHyperLink read to greater than the current READLIMIT setting is disabled by z/OS®. For more information about READLIMIT, see ZHYPERLINK in z/OS MVS Initialization and Tuning Reference.

Not all applications may see a benefit from using zHyperLinks. Review the list of good versus bad candidates before deciding to enable zHyperLinks for a storage class.

Specify values for the following attributes:
zHyperLink Read Eligibility
Specify Y to make this storage class eligible for zHyperLink reads.
Good candidates:
  • Synchronous (blocking) reads where the data is likely to be in the DASD cache.
Bad candidates:
  • Read requests where data is not likely to be in DASD cache
  • Read-ahead or pre-staging of data.
zHyperLink Write Eligibility
Specify Y to make this storage class eligible for zHyperLink writes.
Good candidates:
  • Synchronous (blocking) writes that follow a log write pattern. Writes may wrap around to the beginning of the data set.
  • Block sizes: 4 K or 4K+32-byte suffix for extended format.
  • Data accessed via Media Manager interface.
Bad candidates:
  • Random writes
  • Format writes
  • Lazy/delayed writes
  • Large sequential writes
  • Data sets that contain physical keys
  • Data accessed with EXCP or EXCPVR.