We bought a new Lenovo ThinkServer RD450 rack server.
It has two numbers of 1 GB hard disk. We configured the RAID 1 in the server, and then we started the Debian Jessie OS installation. During the installation, hard disks are not showing in the partitioning step. I tried to boot the system using Ubuntu Live, and in that time I was able to see two hard-disks separately. Please let me know if I should install the RAID driver to detect the hard-disk, and let me know what RAID driver I should use.
What you have there is what's commonly referred to as a FakeRAID controller. This kind of controller combines all of the drawbacks of a hardware RAID card with all the drawbacks of a software RAID.
I would strongly recommend that you use Linux software RAID instead, as it's far more reliable and feature-rich than this could hope to be. To use Linux software RAID via MD or LVM, make sure that you destroy any RAID configuration you've put on that card and then convert it to AHCI or JBOD mode. Or upgrade your card to something that provides an actual RAID abstraction.
These kinds of controllers offload everything to the host OS via a driver, while storing the RAID configuration in the card. This is in contrast to true RAID controllers that have their own small OS and that provide a true RAID abstraction that looks like a single disk to your host OS (and will work with just about any host OS).
Without this FakeRAID driver loaded in your OS, the RAID 110i is nothing more than a pass-through card. Witht he driver loaded, all IO processing happens at the CPU and a special block device is created on the host OS within /dev to interact with rather than the base disks. The RAID members will still be accessible via /dev/sda, /dev/sdb, etc. These should not be touched, and you should only be interacting with the special RAID abstraction block device.
Of course, you need to get the driver loaded before you can address any of this. Ubuntu, having a newer kernel, provides a driver already. However, it's a generic one that won't understand your card configuration or on-disk metadata. In almost all cases, you'll have to download the appropriate driver from Lenovo.
Or you could forget that whole mess and use LVM or Linux MD via mdadm to create RAID block devices.
