One more on that, which I've just thought about:

On Thu, 2013-07-04 at 18:07 -0400, Phil Turmel wrote:

I believe dmcrypt is single-threaded, too.

Even if that is still true... and it with dmcrypt below MD it would run
with _one_ thread _per_ physical device... while the other way round
(dmcrypt on top of MD) it would run with _only one_ thread over the
_whole_ MD device (and thus also all disks)...

...would the former really give a performance benefit (or wouldn't it be
actually much worse).

Since even though you'd have one dmcrypt thread per disk now,... each of
them would have to en/decrypt the "same" actual data for different
devices... so while you have 4x threads... you need to do 4x
en/decryption works.

Which wouldn't be the case when having dmcrypt on top of MD... sure
you'd only have one thread...


Does that sound reasonable?



Cheers,
Chris.