On Sun, 22 Feb 2015 08:33:02 -0600 Alireza Haghdoost [off-list ref]
wrote:

On Sun, Feb 22, 2015 at 6:30 AM, Roman Mamedov [off-list ref] wrote:

quoted

On Sun, 22 Feb 2015 12:31:23 +0100
Christer Solskogen [off-list ref] wrote:

quoted

There are so many different views on the internet

...and yet you're asking for some more? :)

quoted

Is there even such a thing as optimal chunk size?

64K should be fine:
http://louwrentius.com/linux-raid-level-and-chunk-size-the-benchmarks.html

I have seen that people report 64K chunk size results better
performance. However, I was not able to find why mdadm maintainers
decided to switch into 512K default chunk size a few years ago ? Was
that decision related to the write-intent bitmap overhead ?

No, write-intent-bitmap sizing is completely independent from chunk sizes.

I don't remember the detail for the change, but some measurement must have
gone faster with larger chunk size.

single threaded loads tend to prefer large chunk sizes.
multi-threaded small-request random IO tends to prefer smaller chunk sizes.

There is no "Optimal" without reference to a particular work load.  Or
particular hardware.

NeilBrown