LMS blocking on Synology 1517+

Here's something that has been bothering me for over a year now. After
many years of running my own little Linux based server I replaced that
with a (2nd hand) DS1517+ last year. Stronger CPU, 16GB of RAM, 128GB of
SSD cache. You'd think that was plenty powerful to run LMS. Other than
that I'm mostly using Synology Cloud Drive and Moments.

Now my problem is: sometimes LMS would take so long to load even
pre-cached album art, it completely locks up LMS (or it takes so long
because LMS is locking up, I don't know yet). 15-20s of waiting for a
page full of album art, interrupted playback. My Pi3B never shows these
problems!

When this happens I see in top that the CPU is waiting for I/O. Quite
often I/O would be at 60% or more. With the lot of RAM this box has, and
the SSD cache I would have hoped that shouldn't happen. As LMS is the
most actively used app on that box (besides Cloud Drive) I would have
expected its files to be in one of the caches all the time. But no.

Has anybody ever seen similar behaviour on a Diskstation? Or would
anybody know what I should/could tweak to get that beast to behave at
least on par with a Raspberry Pi?... The thought of having to run a Pi
in front of it is kind of frustrating.

--

Michael