Re: [gentoo-user] LVM for data drives but not the OS

[BRM]

----- Original Message ----

> From: J. Roeleveld <joost@××××××××.org>
> On Thu, April 7, 2011 7:31 pm, BRM wrote:
> > The attraction to LVM  for me was that from what I could tell it supported
> > and
> >  implemented a software-RAID
> > so that I could help protect from  disk-failure. I never got around to
> > configuring that side of it, but  that was my goal.
> > Or are you saying I was misunderstanding and LVM _does  not_ contain
> > software-RAID support?
>
> Unless I am mistaken, LVM  does not provide redundancy. It provides
> disk-spanning (JBOD) and basic  striping (RAID-0).
>
> For redundancy, I would use a proper RAID (either  hardware or software).
> On top of this, you can then decide to have a single  filesystem, LVM or
> even partition this.
>
> I think the confusion might  have come from the fact that both LVM and
> Linux Software Raid use the "Device  Mapper" interface in the kernel config
> and they are in the same  part.
>
> Also, part of the problem is that striping is also called RAID-0.  That, to
> people who don't fully understand it yet, makes it sound like it is  a
> RAID.
> It actually isn't as it doesn't provide any redundancy.

I think the issue comes from the fact that LVM2 supports Mirroring without an 
underlying RAID controller:

http://tinyurl.com/3woh2d7
http://en.wikipedia.org/wiki/Logical_Volume_Manager_%28Linux%29
http://www.gossamer-threads.com/lists/gentoo/performance/59776

Which would be a redundancy.

>
> I  do hope you didn't loose too much important data when you had this  issue.
>

No, I didn't loose any important data (fortunately). If I did, I would have paid 
for the drive to be recovered; it was mostly portage, var/tmp, some extra 
sandbox stuff, kind of things.

Ben