On Mon, 02 Jun 2014 11:51:52 +0200 Sebastian Parschauer
[off-list ref] wrote:

quoted

Having a scheduler for RAID0 doesn't make any sense to me.
RAID0 simply passes each request down to the appropriate underlying device.
That device then does its own scheduling.

Adding a scheduler may well make sense for RAID1 (the current "scheduler"
only does some read balancing and is rather simplistic) and for RAID4/5/6/10.

But not for RAID0 .... was that a typo?

Nope, we have our RAID-1+0. So it is more or less a RAID-10 and putting
the scheduler to this RAID-0 layer makes sense for us.

I still cannot imagine how this would work.  RAID-0 has no decisions to make,
so no where for a scheduler to fit.

Just to clarify: is this md/raid0 over md/raid1 or md/raid0 over
hardware/raid1?

quoted

Could you do a graph?  I like graphs :-)
I can certainly seem something has changed here...

Sure, please find the graphs attached. I've converted it into percentage
so that number of bios can be compared to number of requests.

Thanks.

quoted

Show me the code and I might be able to provide a more detailed opinion.

I would say let the user decide whether an MD device should be equipped
with a scheduler or not. We can port our code to latest kernel + latest
mdadm and send you a patch set for testing. Just give me some time to do it.

In the first instance, I just want to get a concrete idea of what you have
done because what you have said doesn't make sense to me.  I'm happy to look
at code against a not-quite-current kernel to get that idea.  But I'm also
happy for it to be against the latest, whatever suits you.

NeilBrown