Re: Raid1 replaced with raid10?

[Neil Brown <neilb@suse.de>]

On Monday May 7, rabbit@rabbit.us wrote:
> Neil Brown wrote:
> > On Friday May 4, davidsen@tmr.com wrote:
> >> Peter Rabbitson wrote:
> >>> Hi,
> >>>
> >>> I asked this question back in march but received no answers, so here it
> >>> goes again. Is it safe to replace raid1 with raid10 where the amount of
> >>> disks is equal to the amount of far/near/offset copies? I understand it
> >>> has the downside of not being a bit-by-bit mirror of a plain filesystem.
> >>> Are there any other caveats?
> >>>   
> > 
> > To answer the original question, I assume you mean "replace" as in
> > "backup, create new array, then restore".
> > You will get different performance characteristics.  Whether they
> > better suit your needs or not will depend largely on your needs.
> 
> Hi Neil,
> Yes I meant take an existing 2 drive raid1 array (non bootable data) and
> put a raid10 array in its place. All my testing indicates that I get the
> same write performance but nearly double the read speed (due to
> interleaving I guess). It seemed to good to be true, thus I am asking
> the question. Could you elaborate on your last sentence? Are there
> downsides I could not think of? Thank you!

I would have thought that you need "far" or "offset" to improve read
performance, and they tend to hurt write performance (though I haven't
really measured "offset" much).

What layout are you using?

NeilBrown