Using HyperPAV for ECKD DASD

The I/O throughput for ECKD DASDs disk can be improved by using Parallel Access Volumes (PAV) or HyperPAV .

z/VM® HyperPAV is also described in Setting up HyperPAV.

The PAV hardware feature is especially important when DASDs are used as data devices with high disk I/O rates, but also as Linux® root devices.

The Linux DASD device driver can use this IBM® System Storage® feature to perform multiple concurrent data transfer operations to or from the same DASD device.

To use HyperPAV, there must be base and alias devices available, which require z Systems® Input/Output Configurations Data Set (IOCDS) definitions. For HyperPAV on an IBM System Storage subsystem, the alias devices are not exclusively referenced to a certain base device but are eligible for all base devices in the same logical control unit (LCU). Linux handles HyperPAV alias devices in the same way as a normal DASD base devices.

The chccwdev command can be used for management or defining the appropriate udev rules for alias devices. When listing the DASD devices with the Linux lsdasd command, HyperPAV aliases can be identified via the alias status tag. The usage of HyperPAV aliases is completely handled by the Linux kernel and transparent to the user.

Note: The sample command that follows indicates that the base and alias devices belong together according to their UIDs.

The following command can be used to display the DASD base and alias devices with their UIDs:

# lsdasd -u
Bus-ID    Name      UID
==============================================================================
0.0.c28a  dasda     IBM.750000000TH031.c280.0a.00000000000075620000000000000000
0.0.c2e0  alias     IBM.750000000TH031.c280.xx.00000000000000000000000000000000
0.0.c2e1  alias     IBM.750000000TH031.c280.xx.00000000000000000000000000000000
0.0.c2e2  alias     IBM.750000000TH031.c280.xx.00000000000000000000000000000000
0.0.c2e3  alias     IBM.750000000TH031.c280.xx.00000000000000000000000000000000

For details about IOCDS configurations, refer to z Systems Input/Output Configuration Program User's Guide, SB10-7037-11a. You can also obtain further information at the IBM Resource Link® Web page (a Sign-On is required):

https://www.ibm.com/servers/resourcelink

For more information about PAV and HyperPAV, refer to How to Improve Performance with PAV, SC33-8414.

https://www.ibm.com/docs/en/linux-on-systems?topic=overview-how-improve-performance-pav

The white paper Oracle Database on Linux on System z® - Disk I/O Connectivity Study describes how HyperPAV can be used with databases. You can obtain this document at this IBM developerWorks® Web page:

https://www.ibm.com/docs/en/linuxonibm/liaag/l0orac00.pdf