Hi Steve,
> Given that we *know* that the UUID is not unique in the multipath scenario,
> and know this at install time, I think it's wrong for us to configure the
> system
> to reference filesystems via this non-unique identifier.
I see your point.
Although, I'm not sure it's technically 'wrong' to do that, given that we're
relying on an udev feature/thing to handle this (which you know, as an
underlying thing, is supposed to work, and actually does).
I guess it's an udev decision/thing to use (sym)link_priority to do this (i.e.,
the by-uuid symlink to a partition in a multipath disk is assigned a higher
priority in kpartx udev rules, and thus the 'active' symlink is that one, until
the multipath disk disappears).
> - 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
There's something almost there being done, but not really w/ an UUID; it has
the device name and partition number in place:
/dev/disk/by-id/dm-uuid-part2-mpath-0QEMU<...>HARDDISK<...>serial_one
Maybe a dm-uuid-part-mpath-<UUID> should address what you mean?
> 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.
May you please clarify? I'm not positive I got it.
AFAICT, for event-driven assembly of multipath devices, it takes calling
'multipath' from an udev ruleset, which is no longer possible w/ recent
systemd-udev (bug 1431650).
And the real problem in this bug (for which the by-UUID problem is a
consequence) is waiting for the SCSI scan to complete, which can't be
guaranteed w/ the current scripts, in my understanding.
Given the case where the root fs is on a multipath device, and it is an
async-SCSI-scan device (e.g., fibre channel), it's hard to tell when all
events/the event of the root fs multipath device is completed. (i.e.,
udevadm settle is not enough).
Even the 'sleep' work-around doesn't guarantee anything -- it just
helps; say, an SCSI scan that takes more than the sleep threshold, on
which the root fs was placed at.
This is an interesting problem.. :)
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https://bugs.launchpad.net/bugs/1429327
Title:
ISST-LTE: system drops to initramfs after install on multipath disk
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