Re: RAID1 and load-balancing during read

[Neil Brown <neilb@suse.de>]

On Tuesday September 11, brederlo@informatik.uni-tuebingen.de wrote:
> 
> I found that near copies behave like raid1, offset copies are slower
> in both reading and writing (beats me why) and far copies are slightly
> faster than near copies in write and twice as fast in read. All for
> sequential read/write. For random writes far copies should be slower
> to write.

I would expect read performance on an 'offset' layout to be
significantly affected by the chunk size.

You probably want the chunk size to be about 4 times the cylinder
size.
The ideal would be exactly the cylinder size, and exactly aligned to
cylinders.  But as cylinder sizes change across the device, this is
not possible.

Unfortunately I don't know how big cylinders are.  I suspect if you
hunt through the docs for the device you might find out.

NeilBrown