Saving updates to a DCSS or set of DCSSs

Ubuntu 22.04 LTS z/VM guest

Use the save sysfs attribute to save DCSSs that were defined without optional properties.

Before you begin

  • Saving a DCSS as described in this section results in a default DCSS, without optional properties. For DCSSs that were defined with options, see Workaround for saving DCSSs with optional properties.
  • If you use the watchdog device driver, turn off the watchdog before saving updates to DCSSs. Saving updates to DCSSs can result in a watchdog timeout if the watchdog is active.
  • Do not place save requests before you have accessed the DCSS device.

Procedure

To place a request for saving changes permanently on the spool disk, write 1 to the DCSS device's save attribute. If a set of DCSSs has been mapped to the DCSS device, the save request applies to all DCSSs in the set.

Issue a command of this form: 
# echo 1 > /sys/devices/dcssblk/<dcss-name>/save
where <dcss-name> is the DCSS name that represents the DCSS device.

Saving is delayed until you close the device.

You can check if a save request is waiting to be performed by reading the contents of the save attribute.

You can cancel a save request by writing 0 to the save attribute.

Examples

To check whether a save request exists for a DCSS device that is represented by the DCSS name MYDCSS: 
# cat /sys/devices/dcssblk/MYDCSS/save
0
The 0 means that no save request exists. To place a save request issue: 
# echo 1 > /sys/devices/dcssblk/MYDCSS/save
To purge an existing save request issue: 
# echo 0 > /sys/devices/dcssblk/MYDCSS/save