Experiments with AutoYaST and Multipath

Some experiments that were performed in order to clarify the real usage of the drive types CT_DISK and CT_DMMULTIPATH and of the parameter general/storage/start_multipath when importing (i.e. applying) an AutoYaST profile in SLE-12-SP4.

See bsc#1130988 for some context information.

All of the tests were performed without bios_id=0x80. You can use edd=off to prevent bios_id to introduce noise in your experiments, although it didn't work in some of my tests. You can also use EFI.

Martin's Scenario

Only one multipath device and only one drive in profile

start_mp	type	MP activated	Device matched	Note
(missing)	CT_DISK	no	first individual disk - sda
(missing)	CT_DMMULTIPATH	no	none
true	CT_DISK	yes	first individual disk - sda	BootStorage err. Missing '/'
true	CT_DMMULTIPATH	yes	multipath device

Imo's scenario A

System with no multipath devices (2 disks)

start_mp	type (/ + /home)	MP activated	Devices matched
irrelevant	CT_DISK x2	no	individual disks, by position
irrelevant	CT_DMMULTIPATH x2	no	error. Why?
irrelevant	CT_DMMULTIPATH	no	first individual disk?

Imo's scenario B

System with one regular disk and one multipath

Important: when multipath is activated, the targetmap contains this (in that order):

• /dev/mapper/QEMU_HARDDISK_0001 - CT_DMMULTIPATH - devices: (/dev/sdb, /dev/sdc)
• /dev/mapper/QEMU_HARDDISK_QM00001 - CT_DMMULTIPATH - devices: (/dev/sda)
• /dev/sda - CT_DISK
• /dev/sdb - CT_DISK
• /dev/sdc - CT_DISK

start_mp	type (/ + /home)	MP activated	Devices matched	Note
true	CT_DM x2	yes	QEMU_HARDDISK_0001 + QEMU_HARDDISK_QM00001
true	CT_DISK + CT_DM	yes	sda + QEMU_HARDDISK_0001	BootStorage err. Missing '/'
true	CT_DM + CT_DISK	yes	QEMU_HARDDISK_0001 + sda	/home (that was assigned to sda) was ignored
false	CT_DM x2	no?	none?
false	CT_DISK x2	no?	it works... but how it matches?

See also https://bugzilla.suse.com/show_bug.cgi?id=1135735 (to be turned into a similar table)