[Bug 1429327] Re: ISST-LTE: system drops to initramfs after install on multipath disk
Mauricio Faria de Oliveira
mauricfo at linux.vnet.ibm.com
Mon Mar 23 13:21:40 UTC 2015
Back to Steve's point (which now I understand more clearly, and looks
totally right..) of event-driven multipath assembly.
> - multipath-tools should (if it doesn't already) create a symlink for the device which includes the UUID,
> but is only ever created once multipath is initialized
> - the fstab and bootloader should be configured to refer to this symlink, not the non-unique UUID
> This should address a number of issues with the initramfs,
> including allowing event-driven assembly of the multipath devices instead of the current blocking script approach.
Some observations..
In the context of relying on event-based multipath discovery.. waiting for the
root filesystem device.. and (not?) booting from an underlying device if it were
supposed to be a multipath device.
----------------------------------
I was wondering whether we would need an 'udevadm settle' after wait-for-root
in order to make sure that any /dev/disk/by-uuid symlink (or any other symlink)
pointed to multipath device at that time (i.e., it could point to an underlying
device if udev rules were still being processed and multipath hadn't run yet).
The answer is 'no', because wait-for-root only receives events from the udev
monitor after all udev rules have been processed.
wait-for-root is OK because it uses "udev" as source identifier in this call:
udev_monitor = udev_monitor_new_from_netlink (udev, "udev");
udev_monitor_new_from_netlink ()
[...]
Valid sources identifiers are "udev" and "kernel".
[...]
The "udev" events are sent out after udev has finished its event processing,
all rules have been processed, and needed device nodes are created.
https://www.kernel.org/pub/linux/utils/kernel/hotplug/libudev/libudev-udev-monitor.html
So, it only receives the event that the waited-for /dev/disk/by-uuid symlink
exists after all udev rules are processed, so it implies that the multipath
command called from udev rules finished, and _if successful_, that the symlink
points to the multipath device rather than the underlying device (the former has
greater link_priority).
In summary, it's not possible to guarantee that the multipath command is always
sucessful; therefore, it is reasonable to depend on a symlink that won't exist
if that command fails (as pointed out by Steve);
for example: /dev/disk/by-id/dm-uuid-partX-mpath-WWID
I'm writing a snippet for /etc/grub.d/10_linux to use that idea, and another
one for the installer to modify /target/etc/fstab to a similar intent, so that
the by-id links from multipath-only devices are used rather than by-uuid of
any disk (non-unique UUID).
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https://bugs.launchpad.net/bugs/1429327
Title:
ISST-LTE: system drops to initramfs after install on multipath disk
Status in debian-installer package in Ubuntu:
Confirmed
Bug description:
-- Problem Description --
We try to install Ubuntu version 15.04 build 20150218 on our system which use the ibmveth for the network and bluefin (lpfc) for this disks.
The Installation completed and ask to continue and reboot, but then it drops to initramfs....
(initramfs) cat /proc/modules
usbhid 63247 0 - Live 0xd000000003520000
hid 128631 1 usbhid, Live 0xd0000000034a0000
lpfc 778399 1 - Live 0xd000000002e30000
dm_multipath 25603 0 - Live 0xd000000002cf0000
scsi_dh 10388 1 dm_multipath, Live 0xd000000002c10000
scsi_transport_fc 71871 1 lpfc, Live 0xd000000002890000
(initramfs) cat /proc/cmdline
BOOT_IMAGE=/vmlinux-3.18.0-13-generic root=/dev/mapper/creeklp1--vg-root ro splash quiet
Look like it cannot fine the vg-root to boot up.
?????????????????????????? [!!] Partition disks ???????????????????????????
? ?
? Note that all data on the disk you select will be erased, but not ?
? before you have confirmed that you really want to make the changes. ?
? ?
? Select disk to partition: ?
? ?
? Multipath mpath0 (WWID 36005076307ffc7b00000000000000717) - 16.1 ?
? Multipath mpath1 (WWID 36005076307ffc7b00000000000000718) - 16.1 ?
? Multipath mpath2 (WWID 36005076307ffc7b00000000000000719) - 16.1 ? ?
? Multipath mpath3 (WWID 36005076307ffc7b0000000000000071a) - 16.1 ? ?
? Multipath mpath4 (WWID 36005076307ffc7b0000000000000071b) - 64.4 ? ?
? SCSI1 (0,0,0) (sda) - 16.1 GB IBM 2107900 ? ?
? SCSI1 (0,5,1) (sdaa) - 16.1 GB IBM 2107900 ? ?
? SCSI1 (0,5,2) (sdab) - 16.1 GB IBM 2107900 ? ?
? SCSI1 (0,5,3) (sdac) - 16.1 GB IBM 2107900 ? ?
? SCSI1 (0,5,4) (sdad) - 64.4 GB IBM 2107900 ?
? ?
? <Go Back> ?
? ?
???????????????????????????????????????????????????????????????????????????
conflicting device node '/dev/mapper/mpath4p1' found, link to '/dev/dm-5' will not be created
conflicting device node '/dev/mapper/mpath4p2' found, link to '/dev/dm-6' will not be created
conflicting device node '/dev/mapper/mpath4p3' found, link to '/dev/dm-7' will not be created
??????????????????????????? [!] Partition disks ???????????????????????????
? ?
? You may use the whole volume group for guided partitioning, or part ?
? of it. If you use only part of it, or if you add more disks later, ?
? then you will be able to grow logical volumes later using the LVM ?
? tools, so using a smaller part of the volume group at installation ?
? time may offer more flexibility. ?
? ?
? The minimum size of the selected partitioning recipe is 596.0 MB (or ?
? 0%); please note that the packages you choose to install may require ?
? more space than this. The maximum available size is 64.2 GB. ?
? ?
? Hint: "max" can be used as a shortcut to specify the maximum size, or ?
? enter a percentage (e.g. "20%") to use that percentage of the maximum ?
? size. ?
? ?
? 64.2 GB______________________________________________________________ ?
? ?
? <Go Back> <Continue> ?
? ?
???????????????
?????????????????????????? [!!] Partition disks ??????????????????????????
? ?
? If you continue, the changes listed below will be written to the ?
? disks. Otherwise, you will be able to make further changes manually. ?
? ?
? WARNING: This will destroy all data on any partitions you have ?
? removed as well as on the partitions that are going to be formatted. ?
? ?
? The partition tables of the following devices are changed: ?
? LVM VG creeklp1-vg, LV root ?
? LVM VG creeklp1-vg, LV swap_1 ?
? Multipath mpath4 (WWID 36005076307ffc7b0000000000000071b) ?
? SCSI1 (0,5,4) (sdad) ?
? SCSI1 (0,0,4) (sde) ?
? SCSI1 (0,1,4) (sdj) ?
? SCSI1 (0,2,4) (sdo) ?
? SCSI1 (0,3,4) (sdt) ?
? ?
? <Yes> <No> ?
? ?
??????????????????????????????????????????????????????????????????????????
????????????????????? [!!] Finish the installation ??????????????????????
? ?
?? Installation complete ?
?? Installation is complete, so it is time to boot into your new system. ?
?? Make sure to remove the installation media (CD-ROM, floppies), so ?
?? that you boot into the new system rather than restarting the ?
?? installation. ?
?? ?
?? <Go Back> <Continue> ?
? ?
?????????????????????????????????????????????????????????????????????????
creeklp2 is now booting. I made a few changes to the system to accomplish this.
First I got the machine to boot by doing the following from the
initramfs:
1. modprobe scsi_dh_alua
2. multipath -v0
3. exit
Once the machine was booted, I did the following:
1. Added scsi_dh_alua to /etc/initramfs-tools/modules
2. Ran update-initramfs to update the initramfs with this change
3. Set GRUB_DISABLE_LINUX_UUID=true in /etc/default/grub
4. Rebuild grub.cfg by using grub-mkconfig
I'm still getting a lot of errors booting the system from udev due to
the fact that udev is spawning a call to multipath for each /dev/sd
device on the system.
I decided to change to not use UUID when I saw in the initramfs that
the /dev/disk/by-uuid symlink was pointing to one of the paths of the
multipath device rather than the multipath device itself.
It seems there may be some udev configuration issues here when booting
from a multipath device.
Can we get someone from Canonical to take a look at this?
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