Re: raid10 layout for 2xSSDs

[Kasper Sandberg <postmaster@metanurb.dk>]

On Mon, 2009-11-16 at 08:08 -0800, Christopher Chen wrote:
> On Mon, Nov 16, 2009 at 6:29 AM, Kasper Sandberg <postmaster@metanurb.dk> wrote:
> > Hello.
> >
> > I've been wanting to create a raid10 array of two SSDs, and I am
> > currently considering the layout.
> >
> > As i understand it, near layout is similar to raid1, and will only
> > provide a speedup if theres 2 reads at the same time, not a single
> > sequential read.
> >
> > so the choice is really between far and offset. As i see it, the
> > difference is, that offset tries to reduce the seeking for writing
> > compared to far, but that if you dont consider the seeking penalty,
> > average sequential write speed across the entire array should be roughly
> > the same with offset and far, with offset perhaps being a tad more
> > "stable", is this a correct assumption? if it is, that would mean offset
> > provides a higher "garantueed" speed than far, but with a lower maximum
> > speed.
> 
> Do you plan to have more than two devices in the array? Raid 10 isn't
no
> magic. If you don't have more than do devices, I suppose your seek
> time might be half for reads (and higher for writes), but you won't be
> able to do any striping.
> 
> I'm a bit confused as to the number of people popping in recently
> wanting to run raid 10 on two disk "arrays".
to get the doubled singlestream sequential read performance..
> 
> cc
>