ZFS weird issue...

[Will Andrews]

On Monday, December 8, 2014, Andriy Gapon <avg at freebsd.org> wrote:
>
> BTW, Will, don't you have a patch that help the vdev phys path to stay
> up-to-date?
>

I don't believe we have any patch for a situation where a member disappears
altogether. Perhaps the best we could do for a situation like this would be
to wipe the physical path in the label for a faulted device, to reduce
confusion.

But a device that's been either manually offlined or physically removed
could come back and be resilvered.

There are patches to provide physical paths through SES/SAF-TE/SGPIO which
offer paths decidedly more physical than a device name. And to perform
automatic replacement by physical path based on these. Not sure to what
degree these have been integrated in the mainline. But this still requires
the system to have an enclosure service of some sort.

Fundamentally, documentation should make clear which /dev device names are
logical and can be reordered due to configuration changes (including device
departure and arrival events) or reboots. As opposed to those based on
immutable properties of the device.

In the case of ZFS, the ideal physical path identifies a slot, so ZFS can
detect when a particular member is being replaced at its physical location
by a new device. So using a device's serial number is a little too specific
for the job. But a typical logical device name is not specific enough.

--Will.