Adding a DCSS device

Red Hat Enterprise Linux 9.2 z/VM guest

Storage gaps or overlapping storage ranges can prevent you from adding a DCSS.

Before you begin

  • You must have set up one or more DCSSs on z/VM and know their names on z/VM.
  • If you use the watchdog device driver, turn off the watchdog before adding a DCSS device. Adding a DCSS device can result in a watchdog timeout if the watchdog is active.
  • You cannot concurrently access overlapping DCSSs.
  • You cannot access a DCSS that overlaps with your z/VM guest virtual storage.
  • On z/VM guest virtual machines with one or more storage gaps, you cannot add a DCSS that is above the guest storage.
  • On z/VM guest virtual machines with multiple storage gaps, you cannot add a DCSS unless it fits in the storage gap with the lowest address range.

Procedure

To add a DCSS device, enter a command of this form: 
# echo <dcss-list> > /sys/devices/dcssblk/add
<dcss-list>
the name, as defined on z/VM, of a single DCSS or a colon (:) separated list of names of DCSSs to be mapped to a single DCSS device. You can map a set of DCSSs to a single DCSS device if the DCSSs in the set form a contiguous memory space. You can specify the DCSSs in any order. The name of the first DCSS you specify is used to represent the device under /sys/devices/dcssblk.

Examples

To add a DCSS called MYDCSS enter: 
# echo MYDCSS > /sys/devices/dcssblk/add
To add three contiguous DCSSs MYDCSS1, MYDCSS2, and MYDCSS3 as a single device, enter: 
# echo MYDCSS2:MYDCSS1:MYDCSS3 > /sys/devices/dcssblk/add
In sysfs, the resulting device is represented as /sys/devices/dcssblk/MYDCSS2.