Obi-Wan Finale - The Loop
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HP Smart Array P212 ZM is known to work flawlessly in the Microserver and it connects directly to the standard SFF-8087 cable coming from the HDD backplane (re-routing of the hdd sas cable is required to reach the connector on the controller  )
- Rosewill RC-211 Silicon Image 2 port SATA II PCI Express Host Controller Card RAID 0/1/0+1/5 JBOD
- Supermicro AOC-USASLP-H8iR (as described in comments - works brilliantly. Also discovered you can put default LSI firmware on it and use the standard LSI Storage Manager software as well. V.happy)
- HighPoint RocketRAID 2720SGL
- HP SmartArray P410. Can be found on ebay or in many other places. Works with SFF-8087 cable. As mentioned in comments - an updated firmware will add support for 3TB drives and 1TB SSD SATA drives. If its configuration contains at least 512MB cache FBWC and Smart Array Advanced Pack license key - it can set even RAID-6 with 4 drives or more. Because you have 2 ports. There is no problem to add external cage with additional power to serve 4 internal + aprox. 12 external drives (cable can be leaded via opened 2nd PCIe bracket). It is important to update it to newest 6.64B firmware. Collect it from HPE site (unlimited access to this FW).