gmirror metadata

[Loren M. Lang]

On Wed, Mar 09, 2005 at 05:43:49PM -0500, Paul Mather wrote:
> On Wed, 2005-03-09 at 21:22 +0100, Pawel Jakub Dawidek wrote:
> > On Wed, Mar 09, 2005 at 03:03:33PM +0100, Michael Riexinger wrote:
> > +> Hi, 
> > +> 
> > +> i have a hp dl320 with an integrated raid controller. I don't want to 
> > +> use that, instead i want to use gmirror. To use the 2 IDE drives, I 
> > +> configured 2 raid0 arrays (each with 1 drive) in the controller's bios. 
> > +> Now i wanted to use gmirror, labeled the second drive. When I did a 
> > +> reboot, the raid controller's bios seems to overwrite the gmirror 
> > +> metadata with its own metadata. Is it impossible to use gmirror witch 
> > +> such a configuration?
> > 
> > I'll be very odd if controller's BIOS overwrite disk data.
> 
> Actually, I had the same type of thing happen to me.  I put a LSI
> MegaRAID IDE 100 that was lying around into my system and attached my
> existing geom_mirrored drives to it.  I didn't want to use the drives as
> an ATA RAID, and never set them up as that in the RAID BIOS.  I simply
> wanted to upgrade from my onboard ATA 33 to the ATA 100 speed the card
> supported, to get faster disk I/O.
> 
> To my surprise and regret, my system wouldn't boot properly (couldn't
> locate the root filesystem) because the ATA RAID card had spammed its
> metadata over the geom_mirror metadata, and my drives were no longer
> detected as a geom_mirror.
> 

I believe one difference between this and Micheal's situation is that,
as I understand it, you created the mirror with a normal ide controller,
then attached it to the raid controller after that, where Micheal
labelled it while it was under the raid controller.  A raid controller
might reserve a sector or track for it's own meta-data, but it should
still provide a slightly smaller disk that would be completely
transparent.  You couldn't see the raid controller's meta-data sectors
nor would any sectors you see or write to be modified by the raid
controller.

> Luckily, I was able to boot from a FreeSBIE CD and re-label my
> geom_mirror with gmirror, thus saving my system.  It was a bit
> disconcerting, though. :-)
> 
> Cheers,
> 
> Paul.
> -- 
> e-mail: paul at gromit.dlib.vt.edu
> 
> "Without music to decorate it, time is just a bunch of boring production
>  deadlines or dates by which bills must be paid."
>         --- Frank Vincent Zappa
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