Re: resync'ing - what is going on

["Jon Nelson" <jnelson-linux-raid@xxxxxxxxxxx>]

On Thu, Jul 10, 2008 at 11:54 AM, Keld Jørn Simonsen <keld@xxxxxxxx> wrote:
> I would like to know what is going on wrt resyncing, how it is done.
> This is because I have some ideas to speed up the process.
> I have noted for a 4 drive raid10,f2 array that only about 25 % of the
> IO speed is used during the rebuid, I would like to have something like
> 90 % as a goal.
>
> This is especially for raid10,f2, where I think I can make it much
> better, but posssibly also for other raid types, as input to an
> explanation on the wiki of what is really going on.

Well, my guess (and from a quick scan of the source) is that basically
raid10 resync by starting at the first logical block or stripe and
proceeds through the last.  This means that there is quite a bit of
seeking going on. IMO, the loop should look more like this:

for component in all_components:
  for stripe_or_block on this component:
    read_or_check_or_whatever(stripe_or_block)

This way, assuming no interference from other sources, each component
does the minimal seeking.

-- 
Jon
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