[PATCH 0 of 13] LVM add 'mirrored' log type

[Takahiro Yasui <tyasui@redhat.com>]

Jonathan Brassow wrote:
> I'm also testing the other approach; that is, allowing lvconvert to take
> non-top-level LVs (e.g. "lv_mlog").  It seems to work just fine.  We
> might want to strongly consider allowing this.
> 
> There are drawbacks to this approach too, however.  For example, when
> one of the devices of the log fails, it will be treated as an 'image'
> failure, and not a 'log' failure (I can fix that though by checking its
> lv->status).  If we decide to go this route, we will have to decide if
> this is the behavior we want or not.  (Once the log is linear, it will
> behave as you would expect - either being replaced or removed according
> to the log policy.)

This approach requires two threads in dmeventd; it is for a top-level LV,
and another is for a mirrored log. If a leg and mirrored log failed at
the same time, a mirrored log needs to be recovered before a top-level LV.
I think this approach is also good if we can handle this situation.

Thanks,
Taka