UCS 4.1 Erratum #82 and UCS 4.0 Erratum #396 added/activated the "savedefault" option by default. This requires GRUB to write to the disk, which is not supported for every type of device (e.g. mdadm-software-RAID)
If GRUB can not write to the disk it displays the message
"Disk filter writes are not supported in boot"
and requires a key press to continue the boot.
As the function does not work if GRUB can not write, the "savedefault" option can be disabled by executing the following command:
ucr set grub/savedefault=false
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GRUB Error: "Disk filter writes are not supported in boot"
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