Unfortunately most small servers from Lenovo, HP, Dell etc no longer have real on-board RAID, it's firmware assisted BIOS raid. AFAICS the Lenovo in question has Intel Intel® RSTe which is one of the above. Real RAID cards cost more than small servers, sadly...
Here's the Intel docs for Linux support:
https://www-ssl.intel.com/content/www/us/en/support/boards-and-kits/000006376.html- which specifies "using Linux* MDADM" ie software RAID. So that's what you use.
A few hints:
1. Don't use RAID 5 if you have SATA disks
2. Really, don't use RAID5 even on SAS
3. Actually just don't use RAID5
RAID5 was wonderful when disks were small, now it will bite you.
More hints:
1. Use RAID1 or 10 or 6
2. Unless you have more than 6 drives use RAID 1 or 10
3. Don't use hot spares without a proper RAID controller and RAID 6 and SAS drives
So if you have 3 SATA drives use them in RAID 1 (with three drives) then it does not fall over in a heap when you lose one drive and the system tries to re-stripe the hot spare causing the other disk to fail
Speaks the Voice of Experience (tm)
MeJ