This is almost definitely a bug in GRUB, but I wanted to get the btrfs mailing
list opinion first.
Symptoms:
I have a btrfs raid1 /boot and root filesystem. Ever since I replaced a drive,
when I run the grub utilities to create my grub.cfg and install to boot sector,
it only recognizes one of the drives.
$ sudo grub-probe /boot/grub -t device
/dev/mapper/VG_BTRFS2-LV_BOOT2
$ sudo grub-probe /boot/grub -t bios_hints
lvmid/gEfhOx-J9hr-8tkA-OgjD-Aqqu-XR2T-sFB4me/oNnMDp-Rit5-P0qs-QZlf-bQQe-tZU7-Wwmz8z
This also prevents boot if the above drive is disconnected. Grub error in
locating
lvmid/gEfhOx-J9hr-8tkA-OgjD-Aqqu-XR2T-sFB4me/oNnMDp-Rit5-P0qs-QZlf-bQQe-tZU7-Wwmz8z
Boot works fine if both drives, or only the above drive is present.
Before drive replacement, the above commands returned both drives that were
part of the RAID1 mirror. I never tried booting with a device disconnected,
but both showed up in my grub.cfg. Replacement was not standard since the
prior drive was developing bad sectors, but had not failed. Replacement was
done by adding a third disk to the mirror, then removing the 1st disk.
Probable Cause:
To determine the boot drive, grub-probe and grub-mkimage make several ioctl in
osdep/linux/getroot.c: grub_find_root_devices_from_btrfs
A call to BTRFS_IOC_FS_INFO gets the max_id and num_devices. It then iterates
from 1 to max_id, calling BTRFS_IOC_DEV_INFO to get the path.
For my system, max_id = 3 and num_devices = 2. Requesting BTRFS_IOC_DEV_INFO
for device 1 yields a "No Such Device". Instead of continuing on to device 2
and 3 (which return without error), grub treats all ioctl errors as fatal,
exits the btrfs specific code with a failure, then falls back to generic linux
code that only detects the single drive.
So, is this a grub bug? If so, any suggestions before I submit to the grub-bug
list? Also, as I wait until a fix is published (or I rebuild grub with my own
patch), any ideas to workaround this?
Info:
Kernel: 4.15.0-12-generic #13-Ubuntu SMP (based on 4.15.7 mainline)
btrfs-progs: 4.15.1-1
Grub: 2.02~beta2-36ubuntu3.17
$ btrfs fi show
Label: none uuid: 84c8e78b-9d7f-4451-966d-3c25154e89b8
Total devices 2 FS bytes used 22.16GiB
devid 2 size 100.00GiB used 25.03GiB path
/dev/mapper/VG_BTRFS2-LV_ROOT2
devid 3 size 100.00GiB used 25.03GiB path
/dev/mapper/VG_BTRFS3-LV_ROOT3
Label: none uuid: 059ab98f-eb63-471d-b099-6561baf39040
Total devices 2 FS bytes used 61.04GiB
devid 2 size 200.00GiB used 62.03GiB path
/dev/mapper/VG_BTRFS2-LV_HOME2
devid 3 size 200.00GiB used 62.03GiB path
/dev/mapper/VG_BTRFS3-LV_HOME3
Label: none uuid: ffe8b1a0-030c-42c2-94f5-b7e8e54b1439
Total devices 2 FS bytes used 342.04MiB
devid 2 size 1.00GiB used 693.62MiB path
/dev/mapper/VG_BTRFS2-LV_BOOT2
devid 3 size 1.00GiB used 693.62MiB path
/dev/mapper/VG_BTRFS3-LV_BOOT3--
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