[Update 2015.10.14] [ND2901] Recommended Hard Drive and using SSD
Update on SSD support at ND2901.
With the improvement of technology, following SSD is proven to be work with ND2901 without external battery.

SAMSUNG 850 EVO series. 1TB.

Working time with the SSD using internal battery was 100 minutes.

ND2901 can be used with any 2.5\\\\\\\' Serial ATA HDD with 9.5mm height.
NextoDI recommend using 5400rpm HDD because of power performance issue.
ND2901 can be used with 7200rpm HDD, but in that case, shorter battery operation time because 7200rpm HDD require much more power than 5400rpm HDD.

The ND2901 or any ND series device needs external battery to work properly with the SSD(specially with the capacity larger than 512GB).
On average, SSDs usually consume less power compared to hard drives but require substantially more instantaneous power when writing to the drive, which the internal battery power system of the ND2901 cannot provide.
See here for getting external battery of ND series.

ND2901 can be used with 2.5\\\\\\\' SATA HDD from any manufacturer. But NextoDI recommend using following HDD which proven to be the most stable 1TB HDD at this moment - May 2014.

WesternDigital : WD Blue series. WD10JPVX or WD10JPVT