Re: raid10 vs raid01 type in dmraid

On Mon, Jun 25, 2007 at 10:18:14AM -0700, Gaston, Jason D wrote:
> >
> >Eg, PC Magazine:
> >"RAID 10, RAID 100 - Speed and Fault Tolerance
> >RAID 10 is RAID 1 + 0. The drives are striped for performance 
> >(RAID 0), and all striped drives are duplicated (RAID 1) for 
> >fault tolerance."
> >
> >Yes, I konw, there's different (aargh!) definitions out there.
> >
> >Like I said: the top -> bottom of the stack definition is preferable
> >to me (you reach the mirror first and the stripe second while walking
> >the stack from the top to the bottom).
> >
> >We just got to hold on to one definition in dmraid,
> >
> >Heinz
> >
> 
> Ok, so the dmraid definition is not going to change.

I'ld much rather avoid it :-)

> 
> Do you see an advantage in putting the RAID1 vs. RAID0 on the bottom for
> being able to perform rebuilds easier?  I need to decide which way to do
> with isw.

Talking about either a mirror on top of stripes or a stripe on top of mirrors,
it is merely a question of IO minimization on rebuilds.

Ie. when a stripe below a mirror breaks, you've got to resilver the whole
stripe set, hence writing 2 or more drives rather than just one disk in
a mirror set beneath a stripe.


With respect to ease of rebuilds at the programming level, there's no
difference in changing the mapping of a top level mirror to do a full
resync vs. a bottom level mirror.


Getting back to your decision: you could support both ;-)

Cheers,
Heinz

> 
> Thanks,
> 
> Jason