clear metadata using dd?

[Reed Loefgren]

Oliver Fromme wrote:
> Hi,
>
> I just noticed this message today, and there's one thing
> I don't understand ...
>
> Fernan Aguero wrote:
>  > I'm trying to set up two disks to contain both gmirrored and
>  > gstriped slices.
>  > 
>  > This is what I'm trying to achieve:
>  > adxs1, swap
>  > adxs2, gmirror
>  > adxs3, gstripe
>
> Can someone please explain why such a setup makes sense?
>
> As far as I can tell, the purpose of gmirror is to provide
> redundancy in the case of drive failure.  I.e. if one
> drive fails, the system keeps running happily instead of
> crashing.
>
> But if only part of the disk is mirrored, then the system
> will still crash if one drive fails.  So what is the point
> of using gmirror, if not on whole disks?
>
> Just wondering.
>
> Best regards
>    Oliver
>
>   
Oliver,

I have gmirror running on my home machine; the entire disk mirrored to a 
second disk, swap included, because that was the setup I followed on 
onlamp's BSD section. In retrospect I would not mirror swap since 
writing to a mirrored swap is a performance hit that might not be 
compensated by the increased read performance of mirrors. I see swap as 
both already slow (compared to RAM) but also somewhat disposable. If I 
were to do it again I would mirror the entire slice (DOS partition) 
holding the OS but leave two slices with the swap partitions on them 
independent, mount both of them with identical priorities, and let the 
OS determine the best usage algorithm. I have a gig of RAM and only 
rarely even touch swap, plus my career doesn't hang on such decisions so 
I can afford to play a bit. Your situation might not have that leeway. :)

r