quick Q about online raid expansion and changing type (QNAP)

hi everyone
i currently have a qnap ts-410 4 bay drive with 4x2tb disks in raid5.
i am building a new server with 6 hot swoppable sas/sata trays.

once i have finished backing up the contents of the 4 qnap disks to a spare server at work (shhh!) i plan to do the following, but am not sure if OMV can do it...
1. build OMV and install on USB stick
2. remove 4x 2tb drives from qnap, insert into new server and configure raid5 across all 4 disks.
3. copy all data back onto the disks (at this point i am assuming the raid5 type from qnap isnt transferrable to OMV without dataloss).

here it where it gets interesting and where i need your help and experience

4. add two 4tb drives to the server, do an online expansion of the raid5 to raid6. at this point i should have 6x2tb logical drives presented as the array (obviously cant use the extra 2tb on the new drives just yet) with two parity stripes.
5. one by one, replace the 2tb drives with a 4tb drive, letting the array restripe from the two parity stripes until i have 6x4tb drives.

would doing the upgrade like this, step for step, result in a final presented array of 6x4tb drives (all space usable) with the two parity giving a usable space of approx 16TB?

so i will have gone from 4x2tb RAID5 to finish with 6x4TB RAID6.

what do you reckon?

the host will be a dell T410 server with lsi 9211-8i sas hba. significantly meatier than the poor qnap t410 which struggles to do much more than NFS!

thanks for your advice, very precise and helpful.
ive just seen about installing to SSD or HD. i have 6 onboard sata ports too so i will grab a small HD from the pile and install on that.

aside from taking a long time to restripe the array (which i can live with) do you see no problem with the approach i have laid out? and that at the end of it i will be able to use the full 4tb capacity?
the drives are 6gb sata, as is the controller and the dual cpu quad core on the server is very beefy, so the rebuild/stripe shouldnt take weeks, just days

thanks for all your help and advise. once the backup is complete (still got 1.4TB to copy off!) i will begin testing OMV in preperation for the new drive purchase

Hello, OP here

I've finally got around to moving all the data from QNAP onto my home server running OMV.
I have had partial success in doing a live move of the disks from the QNAP nas into OMV.
i was able to plug all 4 disks from my QNAP into the server, and through a variety of command line tools (fdisk -l and some otheres i cannot recall right now) the file system was detected by OMV as linux multi-part raid.

the only stumbling block i came across was how to manually create a block device to mount the 4 volumes into. in the end i was pushed for time and had a local backup of the raid contents, so i ended up wiping the 4 disks and recreating another raid5 then copying the data back over.

so basically, if you have a QNAP nas you should be able to bring all the data across to OMV (assuming its ext3/4 formatted) with a little command line expertise. i was pushed for time, but given a few hours more testing im sure i would have cracked the block device creation and mounting the 4 disks as one raid.

i do still have a bunch of spare drives that i was testing OMV with, so if im suitably motivated i can recreate a raid5 across 4 disks and import it into OMV, documenting the steps. just dont hold your breath!!