hi,
new install of OMV 4 on SSD, from bootable usb sitck, on motherboard 775 socket, e8400, 8GB ddr2.
after rebooting, all was fine. Setup in OMV webgui, network, ip address, ... all was fine.
shutdown
install LSi card, 8 sata ports. Plug 8 hdd. setup in lsi bios virtual drive, fine.
boot on ssd... and
mdadm : no array found... messages, a lot. without stopping, until new small OS cli.
a few commands exist in this small reduced os.
i think, OMV tries to boot on my new LSI volume which has never been formatted, because never succeed to run omv gui.
/dev/sda1 is certainly lsi volume. Where is my SSD ? how can i know uuid of my ssd, without disconnecting lsi card ?
maybe i have to install a small omv3 on a new ssd, just to have omv gui, and then having time to initialize lsi volume as ext4 raid 6.
what i don't know is:
how to get debian prompt with unplug anything ?
what is the command line, in small os (i don't remember its name) to access to mdadm.conf on ssd ?
if you have some single steps.
i can try to install on another new ssd, omv5
or older omv3.
in fact all my omv (i have some running systems) are made from OMV3, and were upgraded to omv4, or, the hw raid array were already created and initialized)
it is this reason, i am pretty sure that there is a mistake on omv installer (or debian installer), for new user, who want to run 1st omv install, and then plug new raid volume.
take time, please, to answer or help me, my new big system is initializing raid 6... for a few days 
i am sure the solution is not far...