[Bug 1432060] Re: Include SCSI device handlers for improved multipath support (ALUA, RDAC)

[Mauricio Faria de Oliveira]

The SCSI DH modules are enabled in the kernel config [1]:

	6122 CONFIG_SCSI_DH=m
	6123 CONFIG_SCSI_DH_ALUA=m
	6124 CONFIG_SCSI_DH_EMC=m
	6125 CONFIG_SCSI_DH_HP_SW=m
	6126 CONFIG_SCSI_DH_RDAC=m

Also enabled for the installer's scsi-modules package [2]:

	 125 # device handlers
	 126 scsi_dh_alua ?
	 127 scsi_dh_emc ?
	 128 scsi_dh_rdac ?
	 129 scsi_dh_hp_sw ?

Verified:

	# wget -O scsi-modules.udeb http://ports.ubuntu.com/ubuntu-ports/pool/main/l/linux/scsi-modules-3.19.0-12-generic-di_3.19.0-12.12_ppc64el.udeb && ar p scsi-modules.udeb data.tar.xz | tar tJ | grep scsi_dh
	./lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_hp_sw.ko
	./lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh.ko
	./lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_rdac.ko
	./lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_emc.ko
	./lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_alua.ko

And they are included in the initramfs by default.
It's an effect of 'MODULES=most' in /etc/initramfs-tools/initramfs.conf, which makes auto_add_modules() to copy the entire 'kernel/drivers/scsi' directory.

	# update-initramfs -uv | grep scsi_dh
	Adding module /lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh.ko
	Adding module /lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_alua.ko
	Adding module /lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_emc.ko
	Adding module /lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_rdac.ko
	Adding module /lib/modules/3.19.0-12-generic/kernel/drivers/scsi/device_handler/scsi_dh_hp_sw.ko

Links
	[1] http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-vivid.git;a=blob;f=debian.master/config/config.common.ubuntu;hb=HEAD 
	[2] http://kernel.ubuntu.com/git?p=ubuntu/ubuntu-vivid.git;a=blob;f=debian.master/d-i/modules/scsi-modules;hb=HEAD


** Changed in: multipath-tools (Ubuntu)
       Status: New => Fix Released

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https://bugs.launchpad.net/bugs/1432060

Title:
  Include SCSI device handlers for improved multipath support (ALUA,
  RDAC)

Status in multipath-tools package in Ubuntu:
  Fix Released

Bug description:
  On some SAN storages, the SCSI device handlers ALUA and RDAC help
  linux to handle much more gracefully some I/O errors resulting from
  trying to talk to "ghost" paths.

  Please include those modules (scsi_dh_alua, scsi_dh_rdac) in the initramfs when multipath is enabled
  (i.e., multipath-tools:debian/hooks/multipath IIRC, on a for-loop that calls manual_add_modules() ).

  Thanks to Brian King for providing the information.

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