> Also it is good to know some raid settings such as stripe\block size, write cache mode,
> presence of BBU (battery for internal cache).

Vlad Khorsun! You are my man! :-)
I hope you like the beer I was bringing in Siegburg, because you are
sure in for more!

I took your advice on re-checking cache parameters, and
especially the BBU and found something interesting when reading the
event logs:

That b**ch of a Raid controller reported some error yesterday and -
automatically, without so much of asking me first - reset all caching
params to "highest security", which meant: write through, no adaptive
read-ahead, and a cache size of ZERO!!!

I changed that back again and did some tests and now, after only a few
tests, it looks like some operations take as long as on the old
hardware, but most complex operations with random updates/inserts are
running 4 times faster than on the old system, and some 100 times
faster than with the cache not operating correctly.

I thought it's a LSI, but it's a FTS (Fujitsu Technology Solutions)
with 512MB Cache (which sounds pretty much to me) and so far I did not
find any option to turn off that behaviour of the BBU. Will have a
discussion with the vendor... I don't want the BBU to automatically
set these things for me on any probably not even serious exception.

Stripe size is 64K, btw.

Thanks again,
will do some more tests but looks like I can finish migration to 2.5
next week.