allow_lun_scan parameter default is set to 'on' on SLES12

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Environment

SUSE Linux Enterprise Server 12
SUSE Linux Enterprise Server 12 Service Pack 1 (SLES 12 SP1)

Situation

The allow_lun_scan parameter of the zfcp module, is enabled (set to '1', 'y' or 'Y') by default on SLES12. It is disabled (set to '0', 'n' or 'N') on SLES11.

Instead of having a user-maintained "whitelist" of fibrechannel/scsi disks that are brought online to the guest, the system now polls all the targets on a fabric.

It is a helpful change on systems with hundreds of zfcp disks and exclusive zoning but is rather impractical for systems with just a few disks and an open fabric.
The result of this can be slow boots or access to inappropriate disks in some configurations. It also can lead to administrative difficulties offlining and removing disks if auto-scan is enabled.

Resolution

Automatic LUN scanning can be disabled by setting the kernel boot parameter:
"zfcp.allow_lun_scan" to '0', 'n' or 'N'.

The preferred method to add or change the kernel parameters is by using the YaST Boot Loader Configuration:

YaST - System: Boot Loader. Select "Kernel Parameters" and add "zfcp.allow_lun_scan=0" at the end of the "Optional Kernel Command Line Parameter".

Please note:
When the LUN scanning is disabled, all LUNs must be configured through unit_add in sysfs.

Disclaimer

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