Re: about raid5 recovery when created

[Michael Evans <mjevans1983@gmail.com>]

On Wed, Dec 9, 2009 at 5:43 PM, Neil Brown <neilb@suse.de> wrote:
> On Wed, 9 Dec 2009 19:29:04 +0800
> hank peng <pengxihan@gmail.com> wrote:
>
>> I think it is better to implement this function in kernel's md layer.
>> I wonder what Neil Brown think of this?
>
> I don't think it is worth the effort.
> You probably would save some CPU time as you don't need to XOR, but as has
> been said, we are usually IO bound, not CPU bound.
>
> With the current arrangement, you can start using the array immediately - you
> don't have to wait for the initial recovery to complete.
> If you zeroed all devices at create time, you would have to wait for that to
> complete before using the array.
>
> So I see very little gain, and significant cost.
>
> NeilBrown
>
>

When I assemble an array I tend to have checked the devices before
hand; it would not be difficult to make the final pass a zeroing pass
if I knew I could vastly speed up post-assembly performance.  As I
stated, it's merely a lack of clarity in the documentation.