Broken gmirror: why /dev/ufs is empty when geom_mirror is not loaded?

[Lev Serebryakov]

Hello, Ivan.
You wrote 17 января 2011 г., 16:30:43:

>>>    I have mirrored PARTITION (/dev/ad4s1d + /dev/ad6s1d) with UFS with
>>> label on it. This label is shown in /dev/ufs when geom_mirror is
>>> loaded.
>>
>>>    When geom_mirror is NOT loaded both ad4s1d and ad6s1d are valid,
>>> complete, clean filesystems, but here is no /dev/ufs entries for them,
>>> and kernel can not mount FSes at all.
>>    And even worse: it sees ONE of all FSes and when "geom_mirror" is
>>    loaded, it puck up one of components from "/dev/ufs/home" instead of
>>    device node and everything hangs up due to loop (?)...
> Yes, gmirror and glabel are known to interact badly because of such edge
> cases - since glabel presents the whole underlying device in pretty much
> the same way as the original device entry, gmirror cannot distinguish 
> between the two. You could use the "-h" argument to "gmirror create" to
> get around this.
> Since this is so common and has also bitten me in the past, I wonder if
> some kind of avoidance detection mechanism could be created in gmirror?
  I think, it will be better if geom_label will create ufs/ufsid items
always (even if FS size is smaller that it's container (provider)
size), but create providers only as big as FS itself. It this case
geom_mirror will never see its metadata inside "UFS-based" providers
and geom_label will show FS labels even it it inside mirror when
geom_mirror is not loaded at all. Both problems are solved with one
solution :)

-- 
// Black Lion AKA Lev Serebryakov <lev at serebryakov.spb.ru>