HP Proliant Microserver Gen8: OS on a Micro SD or USB drive a good idea?

I have an HP Proliant Microserver Gen8 and I want to install CentOS 7 on it, to run a Samba server. I've bought two 3TB HDDs for the storage. The OS should be separated from the storage HDDs. So my question is, if it is a good idea to install the OS on a USB drive or Micro SD card?

Use the Intelligent Provisioning (Press F10) feature of this server to upgrade its firmware and gain access to the HP Smart Storage Administrator utility (HP SSA).

• Create a RAID array of your two 3TB drives.
• Create a Logical Drive of a size appropriate for your OS (I prefer 72GB).
• Create another logical drive that fills the rest of the drive array.

That's all you'll need to do. There's no real benefit to using USB or SDHC boot for this.